We do not say "2年間前". Because "間" means "for" in English.so "2年間" means "for 2 years". this sentence means when you start studying English,is not means term.

そうなのか、さとしさんありがとうございます！Seems like I thought the incorrect way of saying was correct the whole time. :P

下の文が正しいです！ You can also say 私は二年間日本語を勉強しています。