I have friends who learned violin when young and, whilst they may not be great players, I have come to realise it gave them many musical advantages, especially over someone like me who learned guitar informally.
   It trains the ear to find intervals, and thus melodies. The dexterity acquired means playing a fretted instrument comes fairly easily. There is a great awareness of timbre and expression.
IMO, learn piano and violin and you are well set up for making and even composing music.