One thing that might be a feasible solution is to ask him whether he can provide these updates through email. This has multiple advantages:

1. It creates a document trail so you can track progress and easily see whether there is evolution in how much he can do and how many problems he has;
2. Reading text is faster than listening to someone speak;
3. If you don't have time, you can simply ignore it;
4. you can tell him to limit his email to a certain amount of lines so he's forced to keep it short and simple;
5. it's asynchronously, so you don't need to both be available.

One thing that might be a feasible solution is to ask him whether he can provide these updates through email. This has multiple advantages:

1. It creates a document trail so you can track progress and easily see whether there is evolution in how much he can do and how many problems he has;
2. Reading text is faster than listening to someone speak;
3. If you don't have time, you can simply ignore it;
4. you can tell him to limit his email to a certain amount of lines so he's forced to keep it short and simple;
5. it's asynchronously, so you don't need to both be available.

Mindwin actually made a very good comment. Instead of sending an email, another good option would be to turn it into a wiki. That way, you don't need to rely on email documents to keep a record. The wiki can be edited by anyone, and the subordinate can be as detailed as he wants.