My DD was quite uninquisitive when she was a toddler, so I never had all the palaver of her climbing up the stairs when I wasn't looking, or in fact wanting to climb them at all really. Shw would only attempt them if I was right next to her, and was quite old before she wanted to go down the stairs herself.
DS (16mo) is a whole different ballgame. If the door to upstairs is left opeen for a second, he is halfway up the stairs before you can blink. I think he is totally too young to negotiate the stairs without me standing behind him in case he falls. I don't think he can understand the consequences.
However, on another thread the other day, a few people said their DCs were going up and down stairs on their own from just over 1yo.
What do you think?