All my babies go up and down stairs fine, that is all except Scampers.
Scampers can go up stairs fine, he zooms right up them. But going down is another story. He is terrified of going down them, he absolutely won't do it. I got tired of him running up the stairs and then whining and barking because he couldn't go down them. So I put a gate up in front of the stairs so he won't be able to go up them and get stuck. I have been working with him on going down stairs since he was 12 weeks old, I did alot of training but it didn't do any good. He is now a year old now and still won't go down the stairs.
The most I have ever gotten him to go down stairs was the last 3 steps on the bottom, other than that you can forget it. Don't know what his problem is with going down stairs but he won't do it. So now anytime I go down stairs I have to carry him.
4 months is young, it took a little bit longer with some of my other dogs so you still have plenty of time to work on it.