Regarding "Jack of all trades, master of none."
Who cares? Being a "master of none" is not a problem the way I see it. Life's just more interesting as a jack of all trades. It's just inherently more fun to pursue interests that excite you without bias. I pick up interests all the time that I never have any hope of "mastering".
I'm always inspired by the stories of 40-year olds who pick up piano. Because of the way cognitive development works, a 40-year old cannot learn piano to the same extent a 10-year old can. But again, who cares?