My hairloss started the same way. It was very thick but started shedding a lot when I was 20. At first it wasn't a big deal because there was heaps left. But I started to see it thinning out and receding and I knew I'd have to do something about it soon enough. I didn't start finasteride straight away. At that time I didn't even know about it. Plus I couldn't have afforded it at the time. But if I'd known about it and I could have bought it, knowing what I know now I would have taken it.
To answer your main question, you're not too young. You should try it and see how it goes. Maybe try taking 0.5mg daily instead of 1mg if you're worried about side effects. One of the great things about taking finasteride is that you feel like you're doing something. It helps you move on and not focus so much on your hairloss anymore. So if your hairloss bothers you then try it and see. If you wait untill your hair is gone then finasteride won't be nearly as effective.
To answer your main question, you're not too young. You should try it and see how it goes. Maybe try taking 0.5mg daily instead of 1mg if you're worried about side effects. One of the great things about taking finasteride is that you feel like you're doing something. It helps you move on and not focus so much on your hairloss anymore. So if your hairloss bothers you then try it and see. If you wait untill your hair is gone then finasteride won't be nearly as effective.