that being said his 40k goes a long way if he retires to Mexico

This depends entirely on WHERE in Mexico you plan to retire. Most Americans view Mexico as a monolith, which is just as false as claiming New York City and Bumblefuck Ohio are the same thing.

The coasts (Cancun, Puerto Vallarta) are already MORE expensive than most "flyover" states in the USA. And although it is true you can find rents ~$350/mo for a small apartment, the standard of living is going to be a lot different than what the typical suburban American is expecting. First and foremost, unless you go to one of the aforementioned tourist spots (which are expensive), being fluent in Spanish is a necessity, and harder to achieve than you may think. Duolingo vocabulary != local slang, idioms and word choice.

I love Mexico. But 40k (800k MXN) doesn't go as far as you think. This is the end result of globalization, friends. Achieving parity isn't a conspiracy theory; it is inevitable.