Certainly more than 100,000 years. From something I read a while ago, anyone born in the 1970's and later has a sufficient chance of living well past 100 years and those born in the 1980's and later, an indefinite life span is possible. I don't recall where I read it, but this was based on our accelerating technological advances. Heh, just ten years down the road and there could be a cure for diabetes, AIDS, or even cancer and 30 years from now, micromachines that destroy harmful pathogens and replenish damaged cells could be highly possible.

Just look at the combination of technological advances from prehistory to AD 1500. Then look at 1500 to 1900. If we brought someone from 1960 to today (such as through a time machine), they could be confused on what things are nowadays. Bringing someone from 1804 to 1904 would be about the same as someone from 1960 to today, even though there is a shorter time span. It's exponentiating, creating a curve in the graph starting off slow but ending extremely fast.

Edit: Big hazards, like a supervolcanic eruption (Yellowstone), a nearby star going supernova, or even a dead, dark star coming along moving planets out of their orbits could all cause major loss in life. Another case, but several million years down the road, would be the Sun getting very hot (but then again, we could change the orbit of the Earth moving Earth further away to cancel this effect).