"If I was born in 1970, I wouldn't say that I was born in the 60s.
Decade = 1960-69, 1970-79, etc...."
Decade then, by redefinition, could also be 1972-1981, the time an aquaintance spent getting his bachelors degree, for instance...
(He said that the school had tenured professors, why not a ten-yeared student as well?)