I think his point was you don't to be "entrenched" in an old stack. How "nimble" your mind is really isn't important, and surely you don't think that a 15 year

I think his point was you don't to be "entrenched" in an old stack. How "nimble" your mind is really isn't important, and surely you don't think that a 15 year old can be more competent than you in a given stack. It's just that you're not exposing yourself to the new stacks.