I assembled this alone, and it is do-able with just one man who is over 50 in age.  I did try calling the toll-free number for help for assembly step 4.  I got no help calling that number.  The D1 and D2 levers would not slide into two holders.  After some time, I resolved this issue on my own.  The fix was to rotate them both 90 degrees.  They slid in easily after rotation.  The rest of the chair was fairly simple to assemble.  Just pay attention to the seat forward arrow on the underside of the seat cushion if you face any difficulty aligning the screw holes (you may have the seat cushion backwards).

The chair feels very comfortable.  However, the wheels included are intended to be used on a carpet and not hard floor or a chair mat ontop of a carpet.  The instructions state you must order a different set of wheels for use on a hard floor.