Women also get more mentally stable in their later twenties. A 19 year old dating a 35 year old is sure to be bat shit crazy and will be unlikely to provide the man with many if any children. A 29 year old woman sees her child bearing years are coming to a end so will be more likely to want and try to get pregnant.

The reason men want young women is because they have many child bearing years but if she won't give children her attractiveness is less imo.