Yes, and yes, to both questions.
No we didn't rent scooters yes there is people with disabilities parking scooters are available all throughout the San Diego area
ADA parking absolutely. Probably on the scooters, I'm pretty sure I saw a couple. However, I would recommend going elsewhere, like the San Diego Zoo, 20-30% of the attractions were closed and we didn't enjoy it. My kids wanted to go home after a couple of hours. They spent the whole day at the zoo and loved it (and it cost us way less too).
There are adult parkings. I'm not so sure about the adult scooters though!
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