Some 1811/special agent/criminal investigator positions in the intelligence community (CIA and DIA come to mind) do not participate in 12d/6c retirement, and therefore do not have mandatory retirement at 57. In theory, this means they'll hire older applicants; I don't know if they have their own age requirements. One significant downside to these positions is that, for some reason, they do not pay LEAP (25% pay bump).
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Not HighSpeed, I may be able to put you in touch with someone who could give more details about the positions I mentioned above, if you're interested.