Is it common to have reading glasses before a certain age?
That certain age being in the mid-40s I presume?
No, it is not common at all. "Farsightedness" means you can see better far off than up close. But the word does not indicate whether that near vison is actually good or not. The farsighted vision problem that requires us to use reading glasses is called Presbyopia. It is qualitatively different than the more usual vision problems of younger people: nearsightedness (myopia) and astigmatism in that Presbyopia is due to the age-related hardening of the natural lens of the eye. [The other vision problems are due to the overall shape of the eye.]
is one other type of farsightedness called Hyperopia (a "too-small"
eyeball). It is much less common than myopia -and unlike myopia does not
typically manifest until later in life. If there more than mild-to-moderate
degree of hyperopia, it is possible a patient years before reaching 40 may
still find reading to be less work with using off-the-rack reading glasses. But
it is really the hyperopia that is being relieved in these cases,
not the Presbyopia