As someone who has a tatoo, and has had it for awhile - I'll chime in here and say that if you choose wisely, you can end up with a fantastic memory that you will love forever and a peace of (hopefully meaningful) artwork to take with you everywhere that will be come as much a part of you as your ears, fingers, and toes. If you choose poorly...you can have something you regret forever...stuck on you for the rest of your life...thats a pretty big choice - not one to be taken lightly...and certainly not one to make based upon the opinions of anyone here...even me.
I chose way too young...I was 16, snuck out with two friends, lied about my age, and got a tatoo. I, however, was very lucky, and made a great desicion that I still LOVE over ten years later.
A small (quarter-sized) shamrock (I'm Irish) on my lower back on the left-hand side that you can just barely see if I wear a string-bikini and not at all in a normal one. I love it, its small and cute and not only means something to me - keeping my heritage close to me...but also is an amazing memory from my somewhat reckless childhood that I will never forget.
However - one of the other girls who went with me thought that a Mickey Mouse face (also quarter sized) on her lower abdomen - right below her belly button on the right - was a good idea. She was wrong...6 months later she told me that it was the worst decision she ever made. When I spoke with her at my wedding she told me that she still couldn't fathom how she could have been so stupid.
My best friend has three...a butterfly on her shoulder, the Celtic tree of life on her lower back, and a 3rd one that I'm totally blanking on right now (lol). She loves them all...each one is a very precious memory to her. I think she is crazy for having tatoos where people can see them...thats just my thing...I love my tatoo...but I know that others don't agree with me and might judge me because of it (for instance in job interviews) so I chose not to put my tatoo on my ankle or shoulder or someplace visible.
In the end...the decision is entirely up to you. The only thing I can agree with everyone else on is this. Think about it carefully. Because you are stuck with this forever (unless you undergo painful surgery which often leaves you scarred). Additionally, choose something that you will treasure forever. And if you decide to go through with it...make a day out of it...bring a friend of loved one...and make it a day to remember!