I can only tell you about the UK and road quads.
In the UK You can have a road legal quad/ATV but it has to have all the road necessary fitments such as lights, indicators, horn, road legal tyres etc and have a certificate of compliance to UK road standards - which you will need to register it with the DVLA and to get it road taxed. it costs the same as a small car to road tax in the UK
You also need insurance, which is quite expensive for a quad - as much as a small car.
The easiest way to get a quad that complies to DVLA standards is to buy one that has all the right fitments already and has a certificate - you can buy them new from about £800 for a Chinese import and a small cc to about £5000 for a good make and bigger cc - but you can sometimes pick up a second-hand road legal quad - try ebay
You can drive a quad of any cc on a full car licence but not on a provisional car licence, then you can only drive under 50cc
You can also drive a quad on a full motorcycle licence
However if you do not have a full car or motorcycle licence theh rules for quads are he same as for motorbikes.
i.e at from 16 you can drive a quad on the road 50cc and under with a provisional Licence and a Compulsory Basic Training ( CBT) license. You have to display L plates
To ride a bigger quad you need either a full car licence or a full motorbike licence.
You do not have to wear a helmet on a quad on the road but I do plus other protective gear as quads can be dangerous if you do not handle them right as they can flip over and cornering them at speed on the road is a lot harder than with two wheel bikes.
Quite honestly as a young person yet to get a licence it would probably be better off to start with a two wheeled bike and get your bike licence under your belt - I have one but they are a lot harder to get theses days. And then you can ride any bike not just quads that have their limitations.
Or concentrate on getting your car licence and then you can ride a quad if you like and you will have the road experience they need