5ft and under should be able to sleep ok on them. My DS aged 12 slept fine on one last May, and he is big for his age. The mattresses are thin and not as wide as a twin mattress, and they are on a rolling board that slides under the beds. Beware1 dont push it under until mousekeeping have been as they may not make it up!
They usually suggest 10 and under. Definately made for a child...our 10 year old granddaughter, who is petite for her age, doesn't want to sleep on one the next time..she had trouble staying on it, it was so skinny. It's just this side up from sleeping on the floor imo.
On our first trip to WDW, my dd was turned 6 y/o. We stayed at POR and she slept in the trundle bed for just 2 nights. She is tall for her age, but the thing that really bugged her was the air close to the floor. She got terrible allergy attacks in the morning. It is very musty on the floor. After she started sleeping with me in my bed, she was fine. Just a thought.
Well, we have stayed in trundle rooms 3 times and all 3 of my kids want to be the one on it. They even came up with a rotation schedule! Last visit, they were DS 12, DD 11, DS 9. All average size and build.
We have some friends who just returned from POR. Their DD slept on the trundle and she's a senior in high school! Another of their DD's had planned to sleep on it (smaller) but the older girl preferred it and was comfortable because she sleeps "bunched up"!
When we crammed 5 people into our room at POR (then DL) my over 5 ft tall DD opted for the trundle bed. She loved it as she sleeps curled up into a little ball anyway. Sometimes when we travel she likes to sleep on the hotel chair and ottoman--go figure!