If it was a group of teenagers would it have been ok to mention it?
Well, since you asked.
"Old people" are adults, just like the op is. There is no need to mention their age at all. If they were 18/19, it would not be ok to say "teenagers" and then have a go at them for trying to be helpful either imo, no. I'd still wonder, "why mention their age"?
If they were 13/14 yos and still children, that's different imo, as they aren't adults. Children are treated differently to adults, legally and socially; children can't vote and you don't put adults in time out for example.
Though, if I was the op and had these comments from children / teenagers / whoever, I would still question why I was getting comments from 4 separate groups of teenagers. I wouldn't start an "oh aren't these teenagers awful" thread. I'd probably think "that's a lot of comments from separate groups. My dcs' behaviour must be quite unusual, or disruptive just now, to have received that many comments from unrelated groups of people".
Not saying tantrums are anything terrible btw. I know it happens. I've got a young dc and lots of nieces and nephews, so I get it. It's just that I wouldn't be blaming the people who commented tbh. Especially if it was four separate groups. Surely they are the least of your worries if you're tackling three grumpy dcs and your mum has apparently undermined you all day. Yet, it's the "old" strangers who get the blame here?