Posted: 05/08/2015 at 18:53
You can pickle the whole green walnut when it is young so by the end of June in most places. There's a recipe here - http://www.davidgregory.org/pickled_walnuts.htm
The ones you've been given will be "wet" walnuts which just means the nut itself is still juicy. Hugh Fearnley-Whittingstall is a fan - http://www.theguardian.com/lifeandstyle/2007/oct/27/recipes.foodanddrink
You can google for more info.
A friend of mine makes a very moist and luscious walnut tea bread with theirs.
There's a recently planted grove of over 2000 walnut trees just up the road from me but they're not ready for harvesting in quantity yet. I'm keeping an eye on them though.