It’s quite common when you are a child to be addressed as ” young fellow “. It’s accurate, not too familiar, and generally not said with any contempt.
Reel on to your senior years – the ones past 60 – and see if you are as happy with the salutation. I get it occasionally from someone who is trying to be familiar but who has not yet established contact. Like the shop owner who addresses me as ” young fellow ” when he is patently younger than myself, and a perfect stranger. He wants my custom but courts it strangely.
I do not react – I never react to it – but I remember it, and mark the shop down slightly. I spend less, if at all.
Note that people who are my same age and are close friends may use it – or any other greeting – freely. In my hobby club we are all of an age and no-one objects to being referred to as old. Indeed no-one bats a wrinkled eyelid at being addressed as ” shithead “. We know our friends and can trade insults freely.
” Old Fellow ” is nearly as bad in a commercial setting. ” Sir ” or ” Madam” are perfectly good salutations in formal society and they can be used with respect everywhere. Age need not be mentioned.