I don’t have anything against young mothers it’s not something I would chose myself because I wanted to travel etc while young. But I can see the benefits.
I've friends on both sides, the big issue for older parent's is support and family connection.
Their DM is older so not in a position to help or enjoy grandchild like she might have in the her 50's/60's.
Also older parents have less healthy time with the children, they could possibly live till 90, less time from future grandchild too.
Most people don't live until 90 and most people have health issues by 65/70.
I don't know about others, from the moment I gave birth, my mindset was to anything to support them. I wasn't young or old 30 and 35 when I had children, my parents died at 70.
I'd like as much time as I can watching them grow
It's also possible to travel and experience things with children.