✨ ベストアンサー ✨
まずI have been playing the piano since I was six years old.が違います。これだと6歳の頃から永遠、何年もピアノを弾き続けていることになってしまうので、l've played the piano~.となります。
二分目・三分目は繋げてBecause of my sister learns to play the piano, I became interested in that too.
以下はこのように英訳しました。
I practiced hard until that day.
I really enjoyed the recital.
I'm still playing the piano.
I want to do my best to get better.