My 6 month old pup still won’t go up or down our inside stairs, and we’ve had him since he was 8 weeks. He will now go up and down porch and deck stairs, so that is something. He has a total phobia - shakes and trembles if you put him down on the stairs, and he just cries and cries if you go up or down without him.
Hoping he gets it soon, because he’s getting to be a big lug to carry around!