To drive a tractor on a public road you must be 16 or over providing you have a full tractor licence. But you will not be able to drive a two seater tractor or one exceeding 20 tonnes.
https://letsfixit.co.uk/16281/what-age-can-you-drive-a-tractor-on-roads-in-the-uk-2/?utm_campaign=twitter&utm_medium=twitter&utm_source=twitter