Are you asking about renting one for a WDW vacatin? There are "special needs" strollers available from at least a couple of the stroller vendors, these are larger and have a higher weight limit to accommodate older/larger kids.
Or are you asking in general -- possibly considering a purchase? I've found Adaptive Mall to be a good resource, it has some good descriptions of various special needs strollers even if you don't buy from them. Also have the mom check out whether their health insurance may cover it. If buying, I suggest they think ahead as to what the needs might be not just now for a 5-yr-old, but also as an 8 or 10 yr old. Special needs strollers are expensive so getting something that will be outgrown in just a year or so can be a waste. If there's thought he may need it for several years, go with a higher weight limit.
When DD was 6 and outgrew a regular stroller, we purchased a used Maclaren Major Elite stroller. We really only use it for vacations now, but did use it occasionally for day trips or special evening community events that had a lot of walking. Her stamina has increased enough that we're good for most single-day events, but on a weeklong vacation we still need it.
Good luck!