The main problem of being married late is the stress of having a child. Not only because it's a great responsibility, but medicine says the possibility of having a healthy baby decreases with age. Maybe not just after 30, but a dream of taking care of a host of own children may not come true. Moreover, couples who have decided to create a full family, may not have enough money to educate their offspring, due to the fact of faster retirement comparing to other relationships.
But there's also a great advantage of getting married a bit later! Both partners have learnt in earlier relationships how to be independent, self-sufficient, and how to accept shortcomings or habits of current beloved one. Another plus is financial stability steady job or even own business. Broadly speaking it's easier to create basis for a partnership, if you've already gained some life experience.
The point is that in fact marriage is about commitment. It is about staying in love and staying together for a lifetime despite the partners age. The challenge of relationship is to make it work, no matter when you get married