In my opinion, barring any sort of medical or mental disabilities, 5 should be the upper age limit for riding in a stroller.
My younger son last rode in a stroller right after he turned 4. We visited WDW that year, a month after his birthday. He did ride in the stroller for the most part, but he also did a fair amount of walking. FTR, this is our "lazy, whiny" kid.
When we got home from that trip, we put away the stroller and then proceeded to visit
Disneyland (as locals) without it. On the day that he went for 6 hours straight at the parks and then went home and spent the afternoon swimming and riding his bike, I knew he was DONE with strollers. Our next trip, he was 5.5, no stroller, and WOW, what a difference! FREEDOM, was what we all felt in not having the stroller. It was great!
That same trip, both kids did great, and about the 5th day, we had some lagging at the end of a long day. We were in Epcot and my younger one just wanted to sit. We sat for a long time, on a bench in Germany near the trains, for almost an hour, but then had to get up to go to dinner at Via Napoli. When he started walking again, he was limping. Turns out, he had some blisters.
He was such a trooper though, never whined or complained about it once, just kept asking to sit down and rest. We patched him up that night in the hotel room and the next day he was good as new. Kids are resilient.