No, I'm pretty serious.
I barely hang out with my friends now. The last time I was to a party that wasn't school related had to be 6th grade or so. I'm a wet blanket.
I believe you, but you're what, 15, 16? Things change. I was living with this girl at the beginning of the year, a first year. Anyway she was a "good" girl. She had friends from school but didn't do much "after hours", studied everyday, called her mum every other day, went home on weekends to help around the house. Then she turned 18 (legal drinking age here) and then every weekend she'd be literally rolling around on the floor drunk, handing in essays late, having loads of people over.
If you are going to go to a college and live on campus, well its like your whole world changes. Most people grow up in a controlled environment, and college is like the opposite, loads of people just going crazy on freedom for a while. It settles but its hard. Even if you don't drink, you're going to want to spend some time making friends and getting into your subjects. You don't want a horse holding you down straight away.
You could lease a horse now and give it back at college. Or if you really wanted to buy a horse you could buy it, lease it out when you go to college, and if you decide you have the time take it back. Just, college is expensive and important, you don't want to screw it up, its easy to say it will be fine now, but its different to what you think. Its not always a walk in the park. Test out the waters before you jump in head first.
What are you planning on studying? What degree you do strongly impacts the amount of "spare time" you have.