Its called the stages of Psychosocial. This all happens in one of the lobes of the brain. Their brain produces high levels of hormones, their emotional side of the brain is still under construction which is normally why they're bratty, ignorant and rebellious. Adolescent Psychology.
Teenagers....ahh. they get into relationships for so many reasons....
-they want to see what the big hype is about...(being love, sex, or both).
-They're exploring, getting older, getting new body parts, and with that comes more hormones, more feelings, more attraction.
-This isn't for all teenagers, but for me, my high school boyfriend and I rushed into it because it was new, exciting, and a first for both of us. We had both experienced our first kiss with each other, both really liked each other, and both were incredibly naive.
-Some do it because of the same old cliche of that's what everyone else is doing.
-Some do it because they're lost, searching for something and someone they can think about before they fall asleep and smile about when they wake up.
There's always benefits to waiting. Most teenagers are too young, too immature, too confused, too insecure, lacking too much self-respect and/or self-confidence to understand what a relationship entails; But then again, that is the time when you're most innocent, and if and when the relationship falls apart, i don't think either person can ever get back that "innocence". After that, i guess people realize how much one person can hurt you, and are never quite the same....they'll never go into a relationship with the same innocence and excitement, or the same open heart as the first one.
Maybe a little too much for an answer, eh? But it's mine, looks like.
Because they're horny as f***
water simply flows downhill - it doesn't wait until it knows where it's going
don't forget that nobody knows what they are doing, once we dig deeply enough
Because they think they're all that and think they're "mature" and is ready when in reality, they're not. Oh I described the younger me...
because of their hormones and it makes them happy.
The bodies develop before the emotional maturity catches up. And the body wants what it wants, so they're often impatient.
Remember that a few centuries ago, when people's life expectancies were about age 30, before getting mauled by farm equipment or dying of typhoid or some other deadly disease, people were expected to marry young. It kept the population going and was good for cheap labour.
These days it just has to do with hormones that have nowhere else to go. This generally happens with girls first. Poor things are practically married to their pillows until one the day the boys' balls drop. Then we're off to the races. Patience is a virtue no one pays attention to any more. Actually, people haven't been paying it any mind for a long time now. There's no retribution for kids' bad behavior anymore, so life's become one massive, non-stop party. This is another subject, though. Unfortunately, people just have to learn from their own poor choices, by which time it's too late. Thanks for the asking the question. I'm truly miserable now.