My experience with foreign exchange have generally been short trips of around two months in the holidays that don't really interfere with the school year. So I'm guessing that yours might be something more like a gap year?
My thoughts on foreign exchange (if it's for an extended period of time for maybe... 7 months>) is that if it won't help you in the future in some way, don't go. I say this because the things and language you've learnt for another country, you'll probably forget if you don't use it again much in the future so it's not exactly a waste of time, but you won't learn much. The things you will get out of it will be the experiences. But, there's nothing stopping you from going to another country at any other time, with maybe better people that you'd like to take along (perhaps a girlfriend? oho). Those experiences can always happen later, and with things like Airbnb now, you can have the same 'authentic' experience of living in someone else's house as well.
But, if you're really looking forward to it, there's no issues if you go now as well.