Longtime contributor Pneumonica won the Immortality Challenge for his extensive work on that topic. As the winner, he got to set the TL for immortality in the next edition of the game. Here it is:
Biotech 6 prevents you from dying due to aging, and from suffering the ill effects of old age, assuming you can visit a doctor on a regular basis.
Add Nanotech 6 if you would like to avoid the doctor's visits - your personal microbots and built-in nanotech take care of such things for you every day.
Add Cognitech 6, with a Mesh, if you would like to do all this and still maintain and manage all your memories. This is the "Terminal Complexity" problem mentioned in the challenge. This note is my addition to his list, but I think it fits well.
Naturally, this will require me to write either a substantial alteration in the skill system, or a more definitive timeline. :) I think the former will probably be in order.