There will be issues with "top-heavy" populations made up much more of older people but I don't see those issues as more insurmountable than the various ways that we are destroying our world with overpopulation.

I used to grieve that my autistic son will never have children, meaning that I'll never have grandchildren. More and more, I breathe a sigh of relief. I don't blame younger people one bit for balking at the world and the life that is being offered to them.