Did you know… Under aged Lords were supposed to inherit their lands when they reached the age of majority which was 18.  In practice the age of majority was fluid.

If an heir was under age (under 21 for a male heir, under 14 for an heiress) they would become subject to feudal wardship, where the custody of their lands and the right to arrange their own marriage passed to the monarch until they came of age.
The wardship and marriage was not often kept in the Crowns hands, it was usually sold to highest bidder, unless outbid by the next of kin.

Held in trust