The human life span has increased by 120% in the last 2000 years. 500 or even 300 years ago it might have been okay for a young person to begin a family at that age because you would only be alive for another 20 years or so. Now, with all of our science, you will probably live another 60 or more years. We can afford to be young for longer, learn more and be pickier about our mates. In turn we will become a stronger species because of it.