Is my rat acting normal?

I had two rats, one was 9 months and the other is 10 weeks old. Unfortunately the 9 month old died due to respiratory problems that was too severe, they said even before i adopted him he probably had this problem. This left the 10 week old alone, so i bought a new companion for him, who was about 6 weeks old and is soo tiny. I've been following the introductory stages for about a week and now i've placed them both in the primary cage. The thing is that the 10 week old rat keeps dragging the little rat into the sleeping quarters and whenever the little rat wants to explore he keeps taking him back and often stays with it. He picks the little one up like a mother would and literally drags it back, which makes the little one squeak but hasn't drawn any blood. Is this normal and should i separate them again? will it lead to aggression or is he being like a surrogate mother to the little one? (who is about 7 - 8 weeks old now) Thanks