By level 30, you'll be destroying everything in your path, killing deathclaws with punches to the face, kicking cazadores to death and stuff. So what about when he gets older. When he hits 50 and his agility drops and he can't use the AMR anymore... What will he (or she if you like) do? Is this far too depressing a thought for New Vegas..?

Nah i think that the courier retires to run vegas and aid the nu-antigoverment he forges. Not much reason to pick up a gun again when you can just have your securtron army slaughter anyone who draws on you.

It all depends on what of person he/she/they are.