I haven't been back to this town for 20 years. It's changed so much and there are lots of new stores here.
この場合、次のような言い方ができますよ。
ーI haven't been back to this town for 20 years. It's changed so much and there are lots of new stores here.
「この街は20年ぶりです。すごく変わって、新しいお店がたくさんあります」
I haven't been back to this town for 20 years.「私はこの街に20年間戻っていなかった」＝「20年ぶりに戻った」と言えます。
ご参考まで！
カナダ 
