Does yahoo delete questions from people that are underage?

You've got the wrong idea. Yahoo didn't come in here and wipe out questions they don't like. Yahoo sets the rules and leaves it up to the members of the community to report content that doesn't belong.
If someone under the age of 13 of posting in here, they don't belong, and the other users should be reporting them.
Call it censorship all you like, but Yahoo makes the rules, and you agreed to follow them. Removing content that doesn't follow the rules is their right.
You must not be too offended, because you're still here...

You must be 13 or over to use this site. If your question indicates you are under 13 it can be marked as a violation by members or the staff. It is up to the staff to close the account.

ℬ ℋ

Yes, though it is we, the users who report violation from underage users (only users 13+ can use this site) and other violating posts

It a person under the age they are breaking the rules for being here, and if they are stupid enough to mention their age then they will be reported as being underage

It is we the users who are the moderators and if enough of us report a question then it is deleted by the Yahoo computer.
It is not a corporate entity as you suggest
Chetak

Yes,their account is suspended.