There are sniper certification courses available, fill out your profile, so we can direct you to the right person for it.
Sniping is well, difficult. I tried it and gave up too much waiting and distance.
there are a few threads about some spring rifles that I suggest you take a look at.
Get age verified, even if your not going to get full on into the sport, its a few minutes out of your life, and people around here seem to have a little more respect if you have the tag.
Personally I would suggest getting yourself a M4 and then slowly over time turning it into a DMR (dedicated marksmen rifle) or sniper hunter. this combines sniping and assault together.
"You know what the chain of command is? It's the chain I go get and beat you with 'til ya understand who's in ruttin' command here."