I think that would be understood in context, but "en los + decade" is mostly used for a time in the century, like in "en los años treinta" (in the thirties).
Yet, now that I think about it, I've heard something like "estoy en mis treintas", "un hombre maduro, en sus cincuentas". However, this is relatively new... due, I guess, to the influence of English. My aunts and grandmother probably would have found it very strange.
