First I'm going to echo everyone else and tell you to go get age verified, it's painless and well worth it.
Now to answer your question, yes you can change FPS rather easily it's just a matter of changing a spring inside the gearbox, a $15 part.
Going up in FPS can sometimes require a stronger motor to accommodate the stronger spring but going down in FPS is usually no problem.
A gun doc can do this for you if you are not comfortable doing it. See this thread to find one in your area