Start lighter and work your way up? The suggestions above for going with a .223 or .243 seem to make a lot of sense.
My personal suggestion for a 14 year old boy would be to go with a classic 30-06 bolt action, a gun he can use for a lifetime to hunt pretty much any large game in North America.
A 14 year old is also going to want a fun range gun too...I'm sure he'd enjoy an AR style black gun. 22LR for lots of cheap shooting, or .223 for the extra bang and option to use it for hunting too.
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