Was thinking of getting one for a eight year old... is this normal?
Respectfully, unless they have a medical issue or are unusually small or frail for their age, no. You'd be hard-pressed to even find a stroller large enough to accommodate an average-sized 8-year-old, except for those designed for children with disabilities.
My kids were 4 and 6 at the time of their first visit to WDW -- at the upper range of typical stroller age. Despite our walking 5-10 miles per day, neither one needed a stroller. Unless you're planning an unusually strenuous itinerary (e.g., park open to park close with no nap, no breaks and lots of criss-crossing the park), a fairly well-rested 8-year-old of ordinary size and physical fitness should be fine without one.
Of course, if you're already getting one for a smaller sibling and it's a question of whether to get a single stroller for the little one, or a sit-and-stand double so their older sibling can hop on from time to time, that might be something to consider, as there's less additional hassle between those two options than there is between "stroller" and "no stroller"...