Seems like a lot of this comes down to making sure you’re enjoying the journey rather than just waiting for the outcome. If you enjoyed being in a band and you grew as a person because of the experience then you didn’t waste any time and that experience will serve you in another way that hasn’t become evident to you. On the other hand if you spent your punk years really only waiting to ‘make it’ and not feeling fulfilled by the experience itself then, yes, it probably wasn’t the best use of your time but strangely, even the ‘wrong’ experiences will still teach is a lot of valuable lessons with hindsight.
I’m not rich or famous but I’ve enjoyed a very varied life in terms of experiences and I don’t regret any of it. As I get older I realise that every single part of my past holds jewels that contribute to who I am and what I can do now. It’s important to remain flexible and lateral in the way we view the possibilities contained in our experiences. We do only see the pattern of the threads with hindsight but it’s a much richer weave than you might imagine :)