These are great points - and yes, old men do get young men to fight their wars... and I have written many advocacy pieces critiquing my country for recruiting at 16... which they can still do (we're the only country in Europe that allows this - and I'm convinced it's against the United Nations Convention on the Rights of Children). However, once someone is 18, we have decided they are cognitively able to make their own decisions, they are functional adults and must respect those decisions, no matter how foolish we think they might be. The army is making them an offer and they have the right to weigh up all the information... we certainly don't keep questioning their decision up through their early twenties.
As for the predatory aspect of seeking younger women, there are always going to be people who behave in manipulative and toxic ways. I glossed over it in the same way I glossed over their equal and opposite number, young women in their late teens and early twenties who will only date men who earn a certain amount and who talk openly about being sugar babies and being spoiled. They are also open and proud of what they do. I glossed over both groups because they're not the norm - though I might go back and address them both in a separate article. In both cases, they're being open about what they're doing and people still choose to engage. God only knows why - but, y'know....adults be adults. So flippers off from this libertarian. :o)