IMO the definition of a vehicle comes down to how wieldy, how large, and how powerful the device is - for instance car is obviously a vehicle as it's very powerful, has a large turning radius, and large area. The interesting thing about this is that there's an argument that scooters are not vehicles but skateboards are - scooters are far easier to control (i.e. more wieldy) whereas skateboards have a tendency to launch the user in one direction and the skateboard in the other, which makes it rather unwieldy.
I would argue it's able mechanical advantage. Everything you listed is a vehicle. Also, skateboards are far more agile than scooters when used by people who know how to ride them. Scooters are just easier for novices.
I would only consider skates to be slightly ambiguous because they are shoes that are mounted but worn. but still, i say vehicle
Rollerblades, skis, snowboards, skateboards, scooters, bikes.
IMO the definition of a vehicle comes down to how wieldy, how large, and how powerful the device is - for instance car is obviously a vehicle as it's very powerful, has a large turning radius, and large area. The interesting thing about this is that there's an argument that scooters are not vehicles but skateboards are - scooters are far easier to control (i.e. more wieldy) whereas skateboards have a tendency to launch the user in one direction and the skateboard in the other, which makes it rather unwieldy.