Go to ur steam, and check for blocked users. You might have accidentally blocked him by mistake.
Re-adding people does not solve this, it must be de-listed.

If this doesn't work, check back later, maybe at night.
I heard steam servers are very buggy these days, especially trade servers. 
But then, this would be a normal thing

ya new account cant trade because that is protect people get scammed by dupe account, if not mistaken need at least 15 days active in steam

u need to verified the account and enabled steamguard. once ur had done this the account will be available to trade after 15 days

http://steamcommunity.com/sharedfiles/file...s/?id=153396149