Ok. Here is the problem, as I see it.
First, what the ATT investigator told you, in order to get you to sign the form, isn't really legally relevant or binding on the company. There is not obligation for them to be truthful in their investigation process. In fact, even police can outright lie to a subject in order to get them to confess (though I've always had a problem with that rule).
The next issue is that you have no personal knowledge of anyone younger than you that has been treated better. Your argument, if you were to make an age discrimination claim, would have to be disparate treatment....which simply means that you have evidence that you were treated more harshly than people younger than you that committed worse offenses and the only reasonable explanation from those facts would be that the employer did so because of your age. To make that argument, you need to be able to point to situations where younger people were treated better and if you have no personal knowledge of those situations, it's going to be difficult to indicate those cases to an EEOC investigator.
Finally, you'll note that I've focused just on the age claim. That is because terminating someone for being highly paid is not illegal in any state or in federal law. It's a completely legal basis to target employees for termination, so it doesn't help you any.
So, to sum up here, you can certainly file an EEOC complaint alleging age discrimination, but you're going to have a very difficult time establishing disparate treatment without clear evidence of younger people similarly situated to you which were treated differently, making it appear to have been motivated by age.