Hello,
Prior FLEO or Military can exceed 37 on initial hire, but straight civilian cannot from what I've seen. The mandatory retirement age is 57 for the 1811(Criminal Investigator) crowd, and 20 years is the minimum for a retirement so that is what the 37 entry age is based off. I've seen higher maximum age limits for hire at some police departments, but can't speak for them.
Mish