I have amblyopia, and I'm almost 18. Will eye patch treatment work?

Probably not. Doesn't hurt to try for a little bit (no downside), but the central nervous system is not as plastic as the peripheral nervous system and typically the visual system has completed development by that age.
Maybe. The optimal age for amblyopia therapy is less than 7-8 years old. The effects diminish with age and by 20 generally no improvement can be realized. It's always worth a try to see what the underlying problem is and begin a course of therapy - there is very little risk of reverse amblyopia.