Lexie learned to go up stairs at about 4 months and weighed about 4lbs, but couldn't go down the stairs till much later. So all day she'd run up then we'd hear the "come get me!" bark and would have to carry her down lol
.That went on for a while till I sat down and clicker trained her to come down, she was so proud of herself she kept running up and down super fast it was hilarious.