Most sources state that electric scooters are not 'road legal' for users of any age.
Quote:
"Electric and petrol-powered micro-scooters are not, and never have been, road legal in the UK. Recent court rulings have imposed heavy penalties on users, treating the machines as small motorcycles in law. Thus, riding an electric scooter in a public place (a public road, footpath or cyclepath) can result in prosecution for riding without insurance, MOT, tax, and a BS-standard motorcycle helmet, resulting in hefty fines and (according to a number of recent cases) points on your driving licence."
Source:
http://www.atob.org.uk/electric_legal_.htm
The suppliers of electric scooters seem to agree with the above statement:
http://www.powerscoots.co.uk/pages/FAQ.htm#zap pyontheroad
However, the Metropolitan Police are of the opinion that electric scooters can be legal for use on roads but only if the user holds a driving licence, wears a crash helmet and displays a vehicle excise licence on the scooter. (They also state that it's necessary to display lights at night):
http://www.met.police.uk/askthemet/514.htm
Chris