It depends on a lot of things, the main one being keeping it out of the sun. But what's the point of getting all these bitchin' sleeve outs if you can't impress the other kids, right?
When I was studying (yes, studying) tattoos, one of the first things that hit me was that the only people in the world who were doing tattoos correctly were the Japanese, as they realized that tattoos simply won't keep detail as the skin is essentially a very slow-moving fluid. The more detail and the more skin sloughing, the quicker the tattoo turns to a nasty smudge. The Japanese deal with this by creating large tattoos with very little detail, and they virtually never expose them outdoors.
One friend of mine was twenty-two when he got a bunch of detailed tattoos on his forearms. By the time he unexpectedly died three years later, his tattoos were totally illegible smudges.
Another thing the Japanese believe, apparently with some clinical evidence, is that tattoos over a significant area of the body tend to somehow reduce lifespan by a few years as they apparently inhibit the skin's ability to perform its organic functions (the skin is the body's largest organ, remember).
