While this is easy to handwave, I'm curious...

A knight with a grant of land and a young son dies. A ward is assigned by the his liege.

1. When does the son inherit?

Upon reaching majority, even if he isn't a knight? Upon reaching majority and being knighted? Upon being knighted, no matter his age? When the liege accepts his oath of fealty?

2. What if the son is eg. blind and incapable of serving his lord as a knight should?

Does the land revert back to the liege, or does someone else inherit instead?

While this is easy to handwave, I'm curious...

A knight with a grant of land and a young son dies. A ward is assigned by the his liege.

1. When does the son inherit?

Upon reaching majority, even if he isn't a knight? Upon reaching majority and being knighted? Upon being knighted, no matter his age? When the liege accepts his oath of fealty?

IMG the normal qualifications are that the heir needs to be of age, have paid the relief (=1 year's income from the inheritance) and done fealty for the land. It is not necessary that they be a knight, but it would be highly unusual if they weren't.

Note that IRL disputes over inheritance (especially how much relief was owed) were one of the principal causes for legal disputes in the period.

Note also that running an estate for a minor is a prime opportunity for the Liege to reevaluate the land and alter the terms of the feudal contract - for example if the predecessor knight had made a number of investments and the manor's now worth £8/year then the heir may well be on the hook for some additional obligations when he inherits.


2. What if the son is eg. blind and incapable of serving his lord as a knight should?

Does the land revert back to the liege, or does someone else inherit instead?

Probably the heir gets passed over, but not necessarily - if the Liege Lord is happy to do it then the heir could engage a retainer to cover the martial side of things and focus his efforts on the 'provide counsel' side of things.

If the 'legal' heir does get disinherited then, of the two options you suggest, the liege lord would generally prefer the first (reversion) but would often settle for the second, for instance if he didn't feel confident about pissing off his other vassals by the precedent he's setting. Or he might 'technically' revert the estate (to show/assert that he can) but then grant it to the next in line to inherit anyway.

The important thing to bear in mind is that it all depends upon what the people involved want to happen - there's always a precedent that can be cited to give you legal cover.

Regards
Luke