What is the average human reaction time?

The median simple reaction time on the Human Benchmark browser test is about 270 ms across millions of attempts. Laboratory studies with calibrated hardware find 200 to 250 ms; most of the gap is screen and input lag. Reaction time is fastest in the twenties and slows gradually with age, by roughly 2 to 3 ms per year on choice tasks.

Source: Woods et al. (2015), Frontiers in Human Neuroscience; Human Benchmark aggregate data (not peer-reviewed)