how long does it take for the stem cell technology being able to treat untreatable illnesses?

Answer 1

Really, it depends on the disease.
Adult stem cell treatment (stem cells from adult tissues, not embryos) has been used to treat over seventy diseases. There is a list here:
http://www.stemcellresearch.org/facts/treatments.htm
However, the time required varies for each disease, and the success rate is never 100%.

Answer 2

A decade.