DS started going up the stairs at warp speed at about 10 months. By the time we moved out of the house (12 months) he was refusing to be assisted in any way, and I had to stay a good three or four steps behind him or he would turn around to shout at me (and only THEN would he fall).... So, I never let him go unsupervised, but unassisted, yes.
Thinking ahead to what it will be like in another year, and if he is as good in a year as he is now at getting up and down, I would definitely let him go it alone. But, that's easy now!!!