Unless your state (FLA.) has a 21 year old requirement or you live in a state that restricts what you can buy you can get any rifle you want at 19. Which one will depend on what you want to do with it. for range fun I suggest a ruger 10/22 or a S&W 15-22 if you want a AR both the ruger ar556 and the S&W M&P sport II are great starting points. big game/deer hunting the savage 110 in 270, 30-06 or 308 will get the job done

Rudy, depends on your state Sir. You can scroll down and check your specific State here (if legal, you can buy any rifle or shotgun)(long gun) : https://lawcenter.giffords.org/gun-laws/policy-areas/who-can-have-a-gun/minimum-age/