Piano is the most comprehensive instrument:
Prepares you for all other instruments
Both hands’ integration
Full view of the entire set of options of tonality (88 keys)
Teaches to read both treble and bass clef
Gives full range for composition and learning music theory
Like anything else, it is faster to pick up while young (although it’s never too late).
Piano and theory can be made fun, children and adults both get a sense of pride and accomplishment when learning to play their favorite songs.
Allows for greater brain plasticity: Music, and especially a versatile instrument like piano, activates multiple integral brain areas at the same time allowing for neuronal pathways to form faster and stronger, with greater cohesion.