you can have 'assisted' passage from the airline which is usually for the less mobile - ie may need someone to push them in a wheelchair, a ride on the golf buggy, platform lift to board aircraft if no airbridge etc. most airlines provide that (or rather the airport!).
No, at EU airports it is the responsibility of the
airport to provide assistance to passengers with reduced mobility. At Manchester you can find information on this
here. Don't think this would include able bodied 16 year olds but ...
Seems the EU boffins didn't like LCCs reducing their costs too much.