Domain Forwarding / Redirection:301 or 302 - Which one is recommended

I got 2 aged domains, both with average DR and DA. I want to build an authority website on one and use the other one for redirecting it to this authority site that will build.

My question is as to which redirection option should I choose: 301 which is Permanent or 302 which is Temp and why?

A 302 redirection is temporary.. If you're doing it for seo purposes then go with a "permanent" 301.