Pup is now 12 weeks.

What age can I let her go up and down the stairs without carrying her?

Thanks

If shw was mine I wouldn't let her until she was a year old.  If you have to, then put her on a lead or hold her collar so you have control of the speed she goes up and down.

With the best will in the world she will get cocky and try jumping up and down stairs several at a time, especially the last few, that is where the damage will be done.

This worried me sick for a while because my house is on a sloping site and has steps to get to the front and steps to get up into the back garden.  If I had carried my pup up and down the steps until she was a year old she would have had no freedom whatsoever in the garden.  I walked her carefully up and down the front steps on lead.  As for the back steps it is funny but I do wonder if a dog has some sense of self preservation in this aspect because she has always made a slide down the plants at the side of the steps.  I do hope that no damage has occured - she is doing agility very happily now at 16 months.   We had Setters before and both learned to use the steps with their long legs.  It is like children with stairs - keep gates at both ends and they don't learn to negotiate the hazard.