personally I think its better to have naturally older characters for a realistic rp, one of my chars is an 8 year old Tabby and I love her too bits!. It gives you a lot more of a story-line advantage to be the experienced wise one of the clan/pack/pride/cult
I don't see a problem with roleplaying elderly characters, much like the rest of you.
I haven't had any really elderly character in a while (My oldest is in the 4-5 range. Unless humans count *cough*). This doesn't mean I dislike them; in fact I am more than willing to create an older character, the problem is that I wouldn't have anything to do with them afterwards and they would probably wind up getting deleted at some point.
I assume most people stay clear of the seniors because they want an OC that will be able fight well, be an eligible mate, and will still have the ability to gallop majestically through a field of daisies with the best of 'em.
But in order to "Roleplay out their lives", wouldn't you need to go through the elder stage, too? My theory is that roleplays don't last long enough for this to happen, or most characters are just killed off at a young age.