The key is to ponder what you can live with for the rest of your life. I have two very tasteful tatoos, both of which were obtained after at least a year of thinking about it. Also, get them in places that are not obvious and can be easily concealed at appropriate times.
I waited until I was 28, had 2 kids, and was getting a divorce to get mine. No-one can see it but whom I want to show it to. It incorporates my kids' names. I have already told my daughter if she ever wants one, she has to wait until she's old enough to know what she wants forever.