Oh, it's always been used (always? a long time, that - but since C19, at the very least)
However, in Southern England in the '40s and '50s, it was definitely looked down on as "lower class" and boys at my school were castigated, but not actually chastised, by the masters for using "haitch" rather than "aitch."

(I don't classify 62 as old, BTW, for very good personal reasons )

The acceptance of "haitch," as I say, appears to be a fairly modern thing in UK.