Anyone regardless of age can qualify for a
DAS based on needs
in the lines. Things which are handled once in an attraction, such as vision or hearing issues, are handled at the attraction itself.
The DAS is for issues not met by the use of a mobility device (Disney mentions wheelchairs and scooters because those are available at the parks, but rollators, walkers, canes are also mobility devices and visual cues you need an accessible waiting experience). For example, I have a whole list of medical difficulties that is not alleviated by my wheelchair (and I have my own custom full time manual). Dangerous things can happen in queues, like my passing out and falling right out of my wheelchair. Some queues are fine, but some are literally impossible for me to navigate safely.
If a patient of yours has a condition that can be helped by the use of a mobility device, even if that means pushing the wheelchair empty sometimes, and sitting when needed (not sitting all day), then they should do so. If there are invisible conditions (ASD, heart problems, mental health issues, etc) that can make it dangerous, unsafe, or impossible to wait in the standard queue, they should ask about the DAS.