That’s the punchline of a famous joke, not a serious argument.
You don’t think it would be true in reality? Predators choose the weakest member of a group to attack, do they not? I know it is a punchline in a joke and couldn’t resist, but also know it would be somewhat true in real life. There are variables, the 30 year old might indeed be stronger/faster than the 20 year old- it happens. My 60 something hubby can easily outrun all of our grandchildren in a foot race- even the ones in their teens. If they get stalked by a tiger it won’t be hubby that gets eaten...
“It’s funny ‘cos it’s true” - Homer