I have not read any info about the life of stainless hoses. The only comment I can give is that as they should not bulge, like rubber ones eventaully will, the life should be longer.
Most people change their rubber lines, as they eventually bulge and you get a reduced performance. I did read somewhere that you should be looking at them carefully after 10 years or so.
However, since stainless ones do not suffer from this, and are somewhat more protected from the elements, due to the sheathing, I would be looking at the state of the fluid when you change it as well as the external condition of the hose. If you see any particulate contamination that could be particles of rubber from the inside of the lines, that is when I would be changing them.
Steve Hawkins