I can see a series of novels covering the young Doctor on Gallifrey, there are young James Bond books for example. Books are not free, but they cost less to produce than TV series or movies.
As Dave says, version of the character that has grabbed the audience for decades is well established and he’s an adult, even if he has looked every age from 20 to 70.
And continuity has never been a big deal for DW. I believe that people can accept more than one version of the Doctor.