Anti-social bristlenose catfish?

I have a male bristle-nose catfish which is about 8 months old and lives in my community tank. When he was smaller, he stuck onto the gl, cleaning away the algae. Now all he does is hide underneath a cave ornament. I never see him come out, day or night. He gets aggressive towards other fish if they go near his cave. My tank is about 60 litres, and is shared with a few corydoras catfish, kuhli loaches, and neon tetras. The temperature is 26 degrees Celsius, and the PH is 7.0. The fish are fed well and there are plenty of plants. Why is he displaying this aggressive and antisocial behaviour?