"jeffbert" wrote:It seems strange that he would wait until about 30 to father his first (& only child), [...]
Not to me...
I don't know how it is where you live, but around here, people are waiting later than ever to have their first child. Many want to finish their studies, live as a couple, get financially comfortable, buy a house and after all that, have children. Many moms want to get settled in their job before getting pregnant. Others, men and women, just don't find the right partner and have to wait.
Of course many young couples have children too, but having less children and having them (or just one) later is more and more common. No wonder why our birth rate is low!
Even in the past generation, I've seen several people around me (friends, neighbors, family) who were born while their parents were older (some moms were even close or past their 40s), and some of them are only child as well. Of course, things could be different in Japan, among other places, but in itself, to me it's a common situation.
As for Tenma, I could totally see him absorbed in his robotics work and forgetting there is life outside of the laboratories, and thus marrying and having his first child past his 20s.

In fact, in the 2003 series, I even have a hard time picturing the lonely and crazy Tenma in a couple, even if at the time he may have been a little less insane since he had not lost his son yet.