When Sully was 10 weeks, he weighed 3.2lbs. We had to carry him up and down the stairs on our back deck to take him out to go pee pee. It was so cute...him trying his very best to do it. Sometimes, we'd let him try and he'd make it up a step or two and then whine for us to pick him up. He was such a "hold me" baby! :-)
Now, he's nearly 8 months old and is about 7 pounds. Maybe 8! (He's really getting big and I'm wondering how b/c his parents were both small!) Anyway, he goes up and down stairs without a problem. He also can jump on and off the couch. Jumping off the bed is no problem, but jumping on is a different story. LOL. He can, sometimes, but our bed is tall for him.
It has been so much fun watching him grow and learn! We used to cheer when he was able to jump on and off the couch and now he does it without a thought.