Black Walnuts

I colleced some black walnuts from the yard.
I'm going to give them to a guy at work, so his wife can cook w/ them.
I've never collected them before, so I had no idea what to look for.
We have several trees so we have thousands of these.
I looked online after picking these up, and found out that you should collect them while the hust is still green. Well, I did not do that... Oh well.
Maybe I'll try to harvest some next year.