Richard isn't ageless by Salem

I'm just new to this site so apologies if this has already been posted. I noticed a few comments about Richard's agelessness and that noone had seemed to come up with a really sound reason.

What if Richard isn't ageless, he just time travels. We know he can get on and off the island to be where and when he needs to be (Locke's birth, childhood visits, Juliet's recruitment...) What if his mode of transport allows him to travel through time (not so far fetched based on what we've been shown in S5)? Someone who is always skipping through time would seem to be ageless becasue they can be anywhere, anywhen. I guess if I use Back to the Future as an analogy. If you didn't know that Doc could time travel, but knew what he looked like in 1885, 1955, 1985, 2015 wouldn't you think he was ageless?

Couldn't Richard be doing all these time travelling missions for Jacob, popping in and out when needed and have only lived a few years of HIS timeline (therefore not changing much in looks) but appearing across a huge span of years, seemingly ageless to the others? Also explains Ben's comments about birthdays - if you spend your life outside of the normal flow of time, then bithdays wouldn't mean anything - how would he keep track of it?