Getting married might be able to limit individual's potential success as marriage requires more responsibilities. But it doesn't mean you can't be successful anymore.
There are several medical studies states that giving birth by 30's could higher the risks for your child to have disorders, which is one of our reason to start an early family.
We still work as professionals and pay taxes and contribute to the economy.
I think giving people more responsibilities can actually make a person more responsible. There's a saying that if you want to get something done, ask a busy person to do it for you. It may seem counter-intuitive. The reason is that somebody who isn't busy isn't used to getting so many things done. Busy people are very good at getting things done.
You make another point that I think is another argument for getting married sooner. If you have healthy children when you are young, without any disorders, then they will soon be working productive members of society. That's definitely better for the economy than a child with disorders that require constant care.