why does the government provide laws for legal ages?

age 16 your legal to drive

Age 18 you have the legal right to vote, to have sexs, to have ur own place, to get married, and to be a legal adult.

Age 21 is legal to drink.

Age 25 is the legal to rent a car.

Age 30 is age when you experience life.

And age 35 is the mature age to want something in life, and legal to be a president.

I don't get ages.how come do you have to wait for these legal age laws? I see people who are 17 or even 18 who drinks beer and liquor and he/she is not even 21 yet. I mean im pretty sure teenagers can handle themselves I mean if their 17, they are an adult. I mean even if they are 15 years old has sexs and they are not even legal 18. I mean I know 15 years old person can handle his/her self. I mean its not like they are a child anymore lol. I also see people who drive a rental car who are in their 20 and they not even 25 yet. So why does age matter? I mean its not like they are not gonna damaged the rental car lol. When they say wait till your 30s to have fully experience life, its not fare. I see people who are in their 20s and even younger than that get married and have baby, especially females who are 15 n they get pregnant!! or even when people who are 13 and they had sexs. Age is just a number. It's not like its gonna be bad thing. I mean come on the government has to be right? Why wait to be 35 to be a president? Why can it be 30 or 25? That's at least old enough. Im 24 yeah im young I know please don't judge me, I was just asking whats true.