The opposite of an Oldfag is a Newfag, both terms are used on imageboards like 4chan.
With regards to /b/, they're the only reason /b/ existed long enough for the newfags to ruin it. We don't want to explain memes to you or guide you away from the trolls. If you don't want to be called a newfag, then sit back idly until you're accustomed to our way of life. Then, an hero.
OF: Sage. Right fucking now.
NF: Stfu oldfag!
They wouldn't stop bitching about the newfags and the "cancer".
What they do best is cry about how good /b/ was.
Oldfag 2: Ruining? /b/ was always /b/ullshit!