If you're saying that he'd have to be crazy to want a toddler bouncing about at his age, I completely agree. However, you're full of chit on the rest of it.
Guys in the late-40s range are typically experiencing their mid-life crisis and do all sorts of stupid things. That's the age where they run off with their secretaries; buy a sports car; rub Propecia into their balding noggins; start wearing skinny jeans. It's a cliche for a reason.
I think the very fact that he's raising his child speaks to his maturity and responsibility.
As far as the crazy ex, her mental state is my inference based on the fact that she gave up her baby. He doesn't call her crazy, to his credit, or bust on her in any significant way. But I am biased, sexist, and judgmental, and think any woman who gives up her child - especially a very young daughter - must be an unstable mess. Your crazy ex being the perfect example.