Exhibit 10.18  David Sinclair Name of Consultant  SIRTRIS PHARMACEUTICALS, INC. Amended and Restated 2004 Incentive
Plan  Restricted Stock Award Agreement  Sirtris Pharmaceuticals, Inc. 200 Technology Square Cambridge, MA 02139  Ladies and Gentlemen:  The undersigned (i) acknowledges
that he has received an award (the Award) of restricted stock from Sirtris
Pharmaceuticals, Inc. (the Company) under the Amended and Restated 2004
Incentive Plan (the Plan), subject to the terms set forth below and in the
Plan; (ii) further acknowledges receipt of a copy of the Plan as in effect
on the date hereof; and (iii) agrees with the Company as follows:  1.             Effective Date.  This Agreement
shall take effect as of January 2, 2008, which is the date of grant of the
Award.  2.             Shares Subject to Award.  The
Award consists of 20,000 shares (the Shares) of common stock of the Company (Stock). 
The undersigneds rights to the Shares are subject to the restrictions
described in this Agreement and the Plan (which is incorporated herein by
reference with the same effect as if set forth herein in full) in addition to
such other restrictions, if any, as may be imposed by law.  3.             Meaning of Certain Terms.  Except
as otherwise expressly provided, all terms used herein shall have the same
meaning as in the Plan.  The term vest as used herein with respect to
any Share means the lapsing of the restrictions described herein with respect
to such Share.  4.             Nontransferability of Shares. 
The Shares acquired by the undersigned pursuant to this Agreement shall not be
sold, transferred, pledged, assigned or otherwise encumbered or disposed of
except as provided below and in the Plan.  5.             Forfeiture Risk.  If the
undersigned ceases to serve as a consultant to the Company and its subsidiaries,
any then outstanding and unvested Shares acquired by the undersigned hereunder
shall be automatically and immediately forfeited.  With respect to any
Shares that are forfeited under this Section 5, the undersigned hereby (i) appoints
the Company as the attorney-in-fact of the undersigned to take such actions as
may be necessary or appropriate to effectuate a transfer of the record
ownership of any such shares that are unvested and forfeited hereunder, (ii) agrees
to deliver to the Company, as a precondition to the issuance of any certificate
or certificates with respect to unvested Shares hereunder, one or more stock
powers, endorsed in blank, with respect to such Shares, and (iii) agrees
to sign such other powers and take such other actions as the Company may
reasonably request to accomplish the transfer or forfeiture of any unvested
Shares that are forfeited hereunder.  6.             Retention of Certificates.  Any
certificates representing unvested Shares shall be held by the Company. 
If unvested Shares are held in book entry form, the undersigned agrees that the
Company may give stop transfer instructions to the depository to ensure
compliance with the provisions hereof.


7.             Vesting of Shares.  The shares
acquired hereunder shall vest in accordance with the provisions of this Section 7
and applicable provisions of the Plan, as follows: 20% of the Shares on January 1,
2010, an additional 30% of the Shares on January 1, 2011, and an
additional 50% of the Shares on January 1, 2012, provided that, the
portion of the Shares that would otherwise vest on January 1, 2012 (the Final
Tranche) will vest as follows, if earlier than January 1, 2012:  (a) one-half of the Final Tranche (25%
of the total number of Shares) shall vest upon completion of a Board approved
corporate partnership for a SIRT1 activator that the Board determines to be significant
for this purpose and (b) one-half of the Final Tranche (25% of the total
number of the Shares) shall vest upon positive clinical efficacy data for a
Sirtris NCE SIRT1 activator as demonstrated by safely meeting the primary
efficacy endpoint of a Sirtris-sponsored Phase 2a or 2b clinical trial in Type
2 diabetes, obesity or a metabolic syndrome.  Notwithstanding the foregoing, no shares shall vest on
any vesting date specified above unless the undersigned is then, and since the
date of grant has continuously been involved as a consultant of the Company or
its subsidiaries.  8.             Legends.  Any certificates
representing unvested Shares shall be held by the Company, and any such
certificate shall contain legend substantially in the following form:  THE TRANSFERABILITY OF THIS CERTIFICATE AND THE SHARES
OF STOCK REPRESENTED HEREBY ARE SUBJECT TO THE TERMS AND CONDITIONS (INCLUDING
FORFEITURE) OF THE AMENDED AND RESTATED 2004 INCENTIVE PLAN AND A RESTRICTED
STOCK AWARD AGREEMENT ENTERED INTO BETWEEN THE REGISTERED OWNER AND SIRTRIS
PHARMACEUTICALS, INC.  COPIES OF SUCH PLAN AND AGREEMENT ARE ON FILE IN
THE OFFICES OF SIRTRIS PHARMACEUTICALS, INC.  As soon as practicable following the vesting of any
such Shares the Company shall cause a certificate or certificates covering such
vested Shares to be issued and delivered to the undersigned without the first
legend set forth above referencing the Restricted Stock Award Agreement. 
If any Shares are held in book-entry form, the Company may take such steps as
it deems necessary or appropriate to record and manifest the restrictions
applicable to such Shares.  9.             Dividends, etc..  The undersigned
shall be entitled to (i) receive any and all dividends or other
distributions paid with respect to those Shares of which he is the record owner
on the record date for such dividend or other distribution, and (ii) vote
any Shares of which he is the record owner on the record date for such vote; provided, however, that any property
(other than cash) distributed with respect to a share of Stock (the associated
share) acquired hereunder, including without limitation a distribution of
Stock by reason of a stock dividend, stock split or otherwise, or a distribution
of other securities with respect to an associated share, shall be subject to
the restrictions of this Agreement in the same manner and for so long as the
associated share remains subject to such restrictions, and shall be promptly
forfeited if and when the associated share is so forfeited; and further provided, that the
Administrator may require that any cash distribution with respect to the Shares
other than a normal cash dividend be placed in escrow or otherwise made subject
to such restrictions as the Administrator deems appropriate to carry out the
intent of the Plan.  References in this Agreement to the Shares
shall  refer, mutatis mutandis,
to any such restricted amounts.  10.           Sale of Vested Shares.The
undersigned understands that he will be free to sell any Share once it has
vested, subject to (i) satisfaction of any applicable tax withholding
requirements with respect to the vesting or transfer of such Share; (ii) the
completion of any administrative steps (for example, but without limitation,
the transfer of certificates) that the Company may reasonably impose; and (iii) applicable
requirements of federal and state securities laws.  2


11.           Certain Tax Matters.  The
undersigned expressly acknowledges the following:  a.             The
undersigned has been advised to confer promptly with a professional tax advisor
to consider whether the undersigned should make a so-called 83(b) election
with respect to the Shares.  Any such election, to be effective, must be
made in accordance with applicable regulations and within thirty (30) days
following the date of this Award.  The Company has made no recommendation
to the undersigned with respect to the advisability of making such an election.  b.             The
award or vesting of the Shares acquired hereunder, and the payment of dividends
with respect to such Shares, may give rise to wages subject to
withholding.  The undersigned expressly acknowledges and agrees that his
rights hereunder are subject to his promptly paying to the Company in cash (or
by such other means as may be acceptable to the Company in its discretion,
including, if the Administrator so determines, by the delivery of previously
acquired Stock or shares of Stock acquired hereunder or by the withholding of
amounts from any payment hereunder) all taxes required to be withheld in
connection with such award, vesting or payment.  Very truly yours,/s/ David Sinclair(Signature of Employee)  Dated: January 2, 2008  The foregoing Restricted
Stock Award Agreement is hereby
accepted:  SIRTRIS
PHARMACEUTICALS, INC.   By
  /s/ Christoph Westphal  3