Paypal is doing this to protect the buyer here. You've been around for some time, but you have not got enough feedback from previous sales for Paypal to be sure you're genuine and not an old dead account that's been hijacked, so they have introduced this to protect buyers from scams - and therefore themselves.
Funds will be released either when the buyer leaves positive feedback, or after 21 days whichever is sooner.
More details here
https://www.paypal.com/uk/cgi-bin/we...utside#payment