I agree with pp saying the kids still need a lot in the secondary years. DH is older than me and has been unemployed following depression and I'm not sure if he will work again. He's 61. We have two DD 12 and 14 - the 14yo has ASD and probably needs more support than the average kid her age. I work 4 days a week and am 50.
While he's been off, DH has been doing the following for the kids:
Lifts to / from school when required (not every day)
Lifts to their activities (6 days a week) and friends' houses
Taking them to any appointments (quite a few for optician and orthodontist)
Taking them out on inset / half term days with friends when I'm working
Helps 14yo with her hobby (sparring)
Obviously there is still a LOT that I do - all comms about school and hobbies and friends, all organising of events and buying of clothes, toiletries etc, most of the help with homework and revision, and the vast majority of their emotional support with friendship dramas.
So it's not like he does everything but it certainly helps that he is able to do the above - previously I would have fitted it in around work, with difficulty, so it is good I don't have to now. There's housework as well of course which i haven't touched on, but even from a parenting pov, there is plenty to do. As pp say, there's then driving lessons and the next move to uni or whatever - parental input definitely needed here.
I think if you can afford it, it is great your DH can retire, but he can and should have a lot of input with his kids - they can benefit a lot from having him around more. It has been really good for my DD14 to have her dad around more. Unfortunately financially it is not so good and he does need to work again, but if he didn't, I wouldn't mind him retiring. I enjoy working, certainly need to work many more years before retiring, and we never expected to retire at the same time.