As others say, it is highly terrain dependent. In my eye, the most relevant factor would be on-trail versus off-trail, and the second would be how high of elevation the climb is. Climbing at 3,000 feet is different than climbing at above 10,000.
Hunting, I'd say 1,000-1,500 is typically a comfortable, normal, relatively easy day. My 10-year old does that without griping. (Too much, anyway.) Heck, my 4-year-old son, 8-year-old daughter, and 10-year-old son did 2,000 feet of gain in about 3.5 hours this summer. (I did carry my 4-year-old a bit, probably 1/2 mile total.)
3,000 feet ican be a pretty hard day. Over that and it gets hard.
I've had a good number of 10,000+ days, not hunting, and mostly on trails. Those are really tough and leave me with sore feet and stiff muscles.
All numbers here are elevation gain, obviously with an equivalent amount of loss.