The age discrimination is real. Whether State Farm has managed to skirt the law successfully is a matter for the courts to decide, and I suggest those impacted take it there.
I know several younger people who took voluntary severance. In every case, they were told some variation of, "No, don't take this severance. This isn't intended for you."
So you have to ask yourself, why would the company OFFER severance to people that it DID NOT WANT to take it? The only logical reason is if NOT doing so would create a legal issue for them, and the only way that makes sense is if the people they REALLY wanted to take the severance were members of a protected class.
I'm certainly no expert on whether one can came age discrimination while simultaneously opting out of the company in exchange for a larger payday. But what I am certain of is that the people SF wanted to leave were identified in large part by their age. Combined with all the stories on this site from people who felt pushed out by targeted management practices (particularly in claims), I am left with the impression that there may in fact be a lawsuit here for those with the patience for it.