You can choose from a number of different companies that run organized trips around different parts of Scotland, cycling together in a group. These tour groups will also arrange your accommodation and you will have the services of a local guide throughout the length of your stay. Most will also offer bike and equipment rentals if you haven't brought your own.
The National Cycle Network is an organization that develops cycle routes throughout Scottish cities, towns and the countryside. If you want to create your own cycling tour of Scotland, then the information they provide on their website will be invaluable. They even suggest certain popular routes that you might enjoy and rate them on their levels of difficulty. Some of the easiest routes also take in some of Scotland's most iconic sights, such as the ride from Edinburgh to the Forth Bridges.
In Scotland, it is against the law to cycle on the pavement, no matter how young you are. Some cities have cycle lanes running alongside regular traffic routes, but at many locations, even busy junctions, you will be sharing to road with cars and trucks. It is not obligatory to wear helmets while cycling on Scotland's roads, even for young people; however, it is recommended that you use these vital pieces of safety equipment.