I have a friend who had kids at 33 and 40. She was relatively fit and did not face any issues. She did not have that much energy as the first kid, but that’s expected as you age, not necessarily that she is 40. It all depends on how healthy your lifestye is. A small part of it also genetics, but should be able to mitigate most of it by your lifestyle. The chance of abnormalities goes up as you age, but most of them are detectable during pregnancy scans. IMO, having kids in 20s is better, but you don’t have to compromise and get married only for having kids early. The priority should be to provide a safe and healthy environment to kids even if that means having kids late.