I've read it twice, and I'm not sure yet why it's smug. I think he is responding to all the backlash that women who are in their 40s keep getting...that they are 'too old' to be parenting children. He's trying to dispel the myth that an older parent is somehow deemed 'bad' by society, and giving examples of why, in some cases, an older mother might have a slight edge over a younger one.
Of course it stands to reason that women in their younger years can absolutely be fabulous mums, there's no question about that. But, there is some validity for what he's saying in some cases.
In my own experience, I absolutely would not have wanted children in my 20's. I wanted to travel,live completely on my own have great friends, be really focused on my career, and I had all that. I had my first DC at 34, and I am much more chilled out, I don't really ever get the urge to go out on a Friday night, and though I am back at uni, I'm fully aware that my career will be second, and I'm okay with that.
Of course, this is only MY experience. But, I don't see why this random guy is being smug just for trying to defend his wife from the constant barrage of press that demeans women who have made the decision to have lives for themselves first, before having DCs.
Sorry...