No, there is no age limit defined for Aadhaar Enrolment. Even a new born baby can also get Enroled for Aadhaar. Yes, once your Aadhaar is generated, you can always download e-Aadhaar letter by clicking on “Download Aadhaar” under 'Get Aadhaar' section of 'My Aadhaar' tab on the uidai.gov.in website