It took almost 20 years from computers that nobody brought on electronics and photography stores to computers in everybody's desk.
Robots will probably be slower, because there is way less room for optimizing their cost.
robots have existed for more than 20 years though. Boston Dynamic's dog is 22 years old, Atlas 15-ish
Mostly just the cost, yeah. It will be like buying a car. The economics will have to make sense for regular people, while it starts popping up in tons of places and become a status symbol.
We have had more than 10 years of robotic vacuums and yet they are still a fairly niche product.