"What is the hardest instrument to learn?"

 What a common question, and the easiest one.

It's your first instrument of course, when you get to grips with the idea of music, scales, intervals, etc for the first time, and reading music as well.

But it's not hard to pick up. I never cease to be amazed by the number of people who then say "I didn't realise that I would learn to read music so quickly". You can get the idea and be reading music onto your instrument within the first lesson.

It's never too late. I couldn't read a note for the first 20 years of my musical life.