42?

"New investigators supported by the U.S. National Science Foundation are also typically 6 to 7 years post-Ph.D. In the biomedical sciences, the average age at which an investigator first obtains a regular research grant from the U.S. National Institutes of Health (NIH) is 42 for a Ph.D. and 44 for MDs. No wonder there is concern about filling the pipeline of scientists. One has to wait until near middle age before getting one's own research program in full gear."
source

Woot, I am only 17 more years from being able to do my own research!

Actually that is pretty optimistic since that number is only those who ever make it to the point they are doing independent research.