The age requirement is 55 for retirement and you would qualify with monthly transfers from a second account. Personally I would not try the money shuffling between a Mexican and US bank. Remember you have to transfer both ways each month unless you have a large savings account that doesn't need to be replenished.

The standard minimum on an ATM exchange is 1% ... and it could be that much or more if your checks are deposited directly to a Mexican bank. They don't exchange for free. Additional fees using an ATM will depend on the US bank you use.

IMSS will be available to you but at a premium with a preexisting condition