I've known several quite young Grumpy Old Sods. It's a philosophical viewpoint, rather than a matter of age - but getting older undoubtedly helps. (And, yes, life-experience counts.)

But not too old - note how my original post began to sound almost mellow towards the end. Richard Bridge also noticed it - but Richard, if you had been in my local this evening (I've just returned from a very Git'ish session), I think you would have approved.