And plenty of young parents have regrets having kids, because they miss out on so much of living for themselves. Not everyone is fit to be a parent, not everyone regrets not having kids, and the way certain people push others to have kids is not done well.

Sharing your personal regrets and experiences of waiting too long to be a parent, while understanding they might not have the same experience; that's fine.

Telling someone they're making a mistake and they're wasting their life or losing time; not fine.

Edit: also, I say this as a parent. I have yet to find a legitimate argument for having kids that isn't based (at least partially) on being selfish. Your comment argues that it enriches the life of the parent. But I think that's a bad reason to have a kid, it's inherently selfish. People who view having kids the same way won't want kids, especially when they understand how fucked up the world is that they'd be bringing their kid into.