6th formers were usually aged 16-18ish (the Sixth Form, unlike the five that preceded it, actually covered two years, divided into lower and upper sixth). The count began at secondary school, so First Formers (or "First Years" as we called them in my day) would be 11 or 12.
The numbering system changed in the 90s and is more like the American one now, I think.
"Dorothy - a baseball wielding ace" - a-ha, the penny just dropped. Took me a while. What a dunce.
