First of all, Congratulations on your future birthday! hehe

Now to the serious point, you're quite young, why aren't you studying? it's not bad to join the police, go ahead if that's your desire but, you're young to take full care of yourself, son don't worry, do as much as you can to grow and be prepared for life
Is perfectly normal not having any idea to what you wanna do, in fact, i'm older than you and i'm in the same boat and guess what? MOST OF US actually still doesn't know, but is what you do with the gift of your life what matters.
Be safe and don't let that depression grow if you can, think of what could you do and also don't let the shadow of you sis outgrows you
You can do it if you propose it to yourself, but remember, it depends on you
Best of wishes