Looking at those '00 Olympia pics, Ronnie's arms are noticeably bigger than Lee's, which are around 20" at contest time. So Ronnie's are around 22" then...not 24". Keep in mind, that adding an extra inch when you've got arms already over +20", is actually a big difference because of the associated "volume" increase with that extra inch. Conversely, say going from 15" to 16", the "volume" increase is not as much. It's just a math principle.
Bottom line is, you gotta be big to have big arms. You won't see 200 lbs. guys with 20" arms. Lee is an extremely rare exception. Of course, superhuman genetics and AAS would have contributed to his outstanding arm development.