Does your SO act like a child? -_-

My SO and I have only been together two months. He does everything right except he's so immature! Given he's like, two years younger than me (which isn't even that much younger so whatever). Hes 20. He will ignore me or storm off when we argue, then come back later to apologize. I like that he says sorry but it'd be nice if he would TALK through things instead of get all grumpy pants. He also farts and laughs all the time, plays Pokemon Go on his phone AND on the game boy, walks ahead of me in a rush every time we're walking or buries his phone in his phone and talks about marriage and kids when we've been together for 2 months!! Lol he's adorable sometimes but he just seems so naive and I wonder if this is something he'll grow out of? Or is he gonna be childish forever?! Urg. 🙄 My last two relationships they were either my age or 3+ years older and didn't act like this lol so I'm hoping he'll grow up eventually