Read paragraph (16) on page 203 of this PDF document from the ATF.
https://www.gpo.gov/fdsys/pkg/USCODE-2011-title18/pdf/USCODE-2011-title18-partI-chap44.pdfThe agent you spoke with is wrong. She apparently got confused about the part referring to replicas of antique guns that are chambered for modern readily available ammunition.
I went through this several years ago when my old FFL Dealer retired and I needed a new guy to do my transfers. The new guy was somewhat confused by the law, so we called the nearest ATF Field Office for clarification. The Agent told us that pre-1899 guns are not even considered as firearms by the ATF, and should not even be entered in the Bound Ledger Book.
Of course, many dealers and sellers cannot and will not be convinced. And you will have little luck getting them to call the ATF for clarification. Please note that some states have requirements that go beyond ATF rules.
The whole thing is kind of silly. An 1898 Parker is OK without an FFL Transfer and Background Check, but the same gun one year newer is not. When the GCA of 1968 established the pre-1899 Antique rule, an Antique was any gun over 69 years old. The date hasn't changed, so now a gun must be 118 years old to qualify as Antique.
