Lots of similarities between you and I, I’d say. A few years ago I had this same frustration. 31 now, same weight. Little shorter. Comparable pace etc. It’s likely multiple things. I used to get very agitated because the rest of my body would feel like I can keep going and going and my feet were starting to hurt baddd at 10 miles. 13 miles would feel like I can’t do more. First and foremost. Your shoes. When I went from boots (even boots I thought were very comfy) to Hoka Speedgoat 5s my world changed. Based on what you’re saying, I don’t think the Altras are for you. Which is already a split decision kind of shoe by the masses. Hokas feel like a got damn temperpedic mattress is strapped to your foot. I frequently do 12-20 mile days (with 25-50 lbs depending on the trips) and my feet while naturally achey given the work - nevrrrrrr hurt like they used too. I loveeeee the Hokas and am hooked for good. People also swear by Brooks. But personally, I want the shoe with the absolute most cushion. Hokas. Particularly the Speedgoats imo. Also, never ignore the comfort benefits of a lighter pack. 5lbs off your back is 5lbs off your feet every step also. Imagine only carrying 20 lbs for example. It’s very very light. Lastly, you simply have baby feet right now as I call it. You haven’t hiked enough yet. The thru hikers don’t get their trail legs and what not until they’re several hundreds of miles in. I do 250-750 miles per year and I’m not in greattt shape till 300-400 miles in. You got baby feet right now and that’s normal. Just have to keep acclimating them to backpacking repeatedly (with the proper gear adjustments) and you’ll be fine. I did a 90 mile point to point trip in Glacier 2 years ago, and a group I was camped with was finishing the CDT same time we were out there. They unanimously thought the first 500 miles was the toughest miles. After you’ve hiked 500 miles, your physically capable of doing damn near any kind of hike. You’re moving major distances nearly every single day. But weekend warriors - you’re doing something tough here and there with many more days of not so tough in between so you’re body gets F’d up when you do it. Keep hiking. Adjust your gear accordingly, you’ll be good.