Sol! Welcome back! We need more Lydiard disciples here!
In an interview with Track & Field News a dozen years ago, Geb indicated that he was unsure of his age, but thought that he was about three years older than "official" records show. The inconvenient problem, however, is that he was thus competing in junior competition when he was no longer eligible to do so. It's amazing that, whenever this issue gets raised, people with no knowledge about the matter come out of the woodwork to defend the accuracy of the "official" records, or react as if it's sacrilegious for anyone to raise the subject.
Bottom line: I think he's about 37 years old. Yes, that's fairly old, but still a bit younger than Carlos Lopes was when he set the world marathon record in 1985.