I hit both ends of the spectrum. Had 4 kids young with my now ex-wife. Was 22, 24,25,27 when I had them. Got re-married at 36, and had our son at age 40.
A couple of things...I'm certainly not as physically capable as I was in my 20's/early 30's. I used to really be able to throw (could hit low 80's pitching, throw a football 55yds)...and now after surgeries to the shoulder...I can't...so my youngest son will never know that part of me, or who I once was. I could run pretty good...but age and a torn achilles...not so much. So that part is sort of sad to me...not the aging, as that's expected, but he won't ever know how capable his Dad once was.
I actually think I handled the sleep deprivation better the second time around. I always took my nights with the kids (we would switch off nights, so one of us could be fully functional the next day). That could be as I progressed in my career (chef), I did less of the physical work, could be as I got older, I didn't need as much sleep, or most likely it's because I was more stable in both life and career. I eat better, don't stay up late, don't get stressed out as much about things I can't control, etc.
I'm much more patient this time around. Trying to get to root causes of any issues (behavioral, sleep, school, etc.) than I was the first time around. I was much more reactionary and probably "old school" in discipline (never spanked, but grounded, perhaps yelled, etc).
Certainly, have more disposable income (well, $1 would be more than I had with the first 4), so can do more "stuff"...but that can build up expectations with our son (he thinks he should fly first class:) Being more established in my career has also allowed me to be more involved with his school, coaching, building projects(tree fort), etc.