You Just Broke Your Child. Congratulations.

My wife and I are welcoming our first child into the world next year. I am 42 and she is 41.

I honestly think I will be a much better parent now than at age 25-30. I have learned so much in the last decade and a half. I know that in stressful moments I fall back onto the way I was raised. Back then I thought yelling and name calling was normal. But at least I know it and I actively TRY not to act that way.

Sometimes I snap at my wife during an argument the way he used to and it just makes me feel like total crap. I gotta get that TOTALLY under control before the kid comes. I never want to treat my kid the way I was treated.

It's not that my folks were bad people, but they had ZERO idea how to raise a child. It was very much a "spare the rod" kind of upbringing. They thought they were doing it right and I turned out OK in their eyes so they feel justified. They have no idea the baggage I carry from all those experiences.
40 is when I had my first - I might have been able to parent ok in mid 30s but certainly not before that - I still had way too much play in me
I think the major trade off with starting later is having much less energy/stamina for play, et al

I’d caution against trying to eliminate ‘snapping’
You’ll be stressed and exhausted and learned behavior will seep out - no need to add guilt and disappointment on top of that - talk it through with your wife about how to check each other and help quickly navigate away from the behavior you don’t want to display