I want to wait at the gate to pick someone up can I do this?

Unless it's an unaccompanied minor if not....no

Nope. Not unless you get permission from the airline for specific reasons.

No

I am not sure about a "pass" but security has let is go to the gate with a minor so if you ask they may let you wait for an arriving minor too. They are usually accommodating for minors. Others not so much.

If you are picking up an unaccompanied minor you can get a gate pass to get through security, otherwise you will have to wait outside of security for anyone else.