To put it very simply, quantity and quality. It also matters what people claim to be a veteran of don't you think? Claiming to be a veteran member would be different from claiming to be a veteran Hand or Crew Leader. Years do count for something, because even the slowest learning person will have mastered what being a member means if they've been playing for a few years (I'm speaking hypothetically and looking at extremes here). Thus they become a veteran member by virtue of quantity. Others pick up everything there is to the game in a couple of months. They would become veteran members by virtue of quality learning. The same principle applies to being a veteran Hand, CL, or Godfather. A third factor could also include the network of friends you've made. Can't underestimate the value of a good network in this game. This would require quantity, quality, or both. I hope this helped.

I think you've covered it already. Being a Vet is based purely on what you've done with your time here. If you just sit around and click buttons and don't do anything with your character, then repeating this for years on end doesn't make you a Veteran. (Nor is such a practice necessarily bad, plenty of players aren't interested in the main aspects and simply click about whilst chatting to friends)

There are plenty of players that can/should be regarded as Vets, to me those are the ones I can recall from the days of old .org, names like Gazman and Jono to name a couple. There are loads of them around here still i'm sure, I myself started playing back in Feb 2002, I'm sure there are some here that would have been before me (Shuki still roams around im sure?). - people of such longevity generally have done more than others, purely because in that time they've had the chance to achieve more. So you'll likely find older players are the more so Vets amongst us.