What you are comparing is widly different. You could not join the marine corp, nor could anyone else your age. But you were able to be fond of it and prepare for when you were old enough to join it. You could dress up like a Marine, read about Marines, and learn how to prepare to be one. You couldn't drive a car, but like a Marine, you could express your interest in cars in many ways. No one was going to wag their finger and say how dare you show interest in cars. Beer and guns are for safety reasons. Mind you, many parents let their kid try beer before the legal age. They say, what's the harm in a small amount. I don't have a problem with that either. Do you? A parent may teach a kid about guns, how to use them, and even let them use one. Honestly, if done with precaution and care, again I do not mind it. Maybe not when they are super young, like 7 years old. But 14? Why not I say?
But here's what you are failing to understand. When you are a young boy and you have these interests, they are being supported. You want to play cops and robbers? Have at it. You want to collect hot wheels cars and make "Vroom Vroom" noises with them? No problem. You want to dress up like your favorite Marvel hero, say Iron Man or The Hulk? Sure, that's okay. You want to hang Marine posters all over your room? That's swell. You want to tell everyone that you hope to be the next Chuck Norris when you grow up? Okey dokey. You are supported.
But then there is Billy. He wants to pretend to a damsel in distress and have his dad save him. His dad says no, boys don't do that. He wants to play with barbie dolls. His dad says no, boys don't do that. He wants to dress up like Elsa from Frozen. His dad says, no that's a girls costume. He wants to hang posters of dreamy boys who star in teen romance shows. His dad tears them down, and says those are girl posters. He tells everyone that one day he hopes to be just like Taylor Swift, a powerful woman. Everyone laughs at him. His dad is embarrased by him and hardly wants to talk to him anymore. Billy is struggling because he keeps being told he cannot be who he wants to be. He feels lonely and sad, and thinks there must be something wrong with him. Billy feels this world is not meant for him. Billy takes his own life.
You see, your interests and who you are are supported. There may be restrictions, but these are the same for anyone else your age. But for Billy, he is being told he cannot do, say, and feel things because others feel they are not right to feel, while if he wanted to do, say, and feel things that were in line with the standard expectation our society has placed on boys, then it would be okay. This is not a fair and equal situation. You are not being crushed for your interests. Billy was, and now Billy is gone because no one supported him.