Here's a small meditation on the permanence of tattoos for you:
1. Think of something you thought was really cool. The GREATEST! Ten years ago. How do you feel about it now? Ten years ago I was going to be a doctor and teach a certain style of karate in my imaginary weekends. I loved American cars. I'd cut off a limb that contained artwork referring to any of those three things now.
2. Tattoos aren't actually permanent. They fade and change over time, even if your body never changes shape, which it's more likely to do than not. You can keep it out of the sun to minimize fading, but then you're hiding your tattoo, so why did you get it?
Do whatever, I'm not actually trying to dissuade anyone, but these two observations dissuaded me. It's a good thing they did too, because I wanted a forearm tattoo and given my current job I'd be wearing long-sleeved shirts in the hideous southern Japanese heat every day if I had gotten it.