I think there can be quite a variation, regardless of age. I'm less than a week back home now from a 5 week trip hiking half of the Florida Trail. I'm 58, my hiking partner is 66. I have a hard time keeping up with him. We had another friend who did the first 3 or so weeks with us, he's also in his 60's.

Florida is pretty flat, but hiking in January there's a limited number of daylight hours. Starting out we hiked lower miles; still, we did 14 miles our 3rd day out. 19 miles the 4th day, and by the second week we had settled on "low twenties" as what we shot for each full hiking day. After we were fully up to strength, it was more typically the amount of daylight that limited us to this.

My point is that age alone isn't an automatic predictor of lower mileage. In the long distance community, often it seems like the older hikers do as many miles per day as the young folks do. We just do it differently. They'll sleep in, take long breaks, etc, whereas the older hikers get up with the dawn and just sort of "keep going". To be clear, average sustainable hiking *speed* will be higher for younger hikers --- definitely. But I think that miles per day is a better metric to consider than average walking speed (which is just one factor in MPD).

Not for everyone, but don't automatically lower your expectations based on age if you're overall in (or can get in) good condition. A lot is based on "style" and expectations, process. And, of course, total pack weight (these are all related).

Best wishes regardless of the approach that works best for you!
_________________________
Brian Lewis
http://postholer.com/brianle