I don't resent his decision to have children at that age, in and of itself. But what I do resent is that he had children at that age, but wasn't willing or able to make corresponding adjustments to his own life.
I never played catch with my dad. It wasn't his thing.
He rarely came to school events. They weren't his thing.
My childhood included constant reminders that he was too old to be doing X, and I should not expect him to live until the next major milestone, so I should just appreciate the time we have left and not push it. He ended up living until 95, so he was alive for a lot of milestones, like when I graduated high school and college, got married, and had children. But for the vast majority of my life, he was more like a grandfather than a father.
My advice to anyone who's thinking of having kids later in life: Be willing to keep up with the 30-something moms and dads out there. Do whatever you can to remain youthful in spirit. Throw out your retirement plans, because until the kids are out of the house, you are ON DUTY. And take some time to toss a ball around every once in a while.