Actually, we all know that bifocals can correct far-seeing vision and near-seeing vision. It Is mainly used to those who both have myopia and presbyopic, and there is obvious line between myopia lens and presbyopic lens. So, bifocals generally just help correct vision. But age is not the decision factors about myopia or presbyopia. If you must find a relationship between age and bifocals, now young people are easier to get myopia, and middle-aged, general above 40 years old people are likely to suffer from presbyopic. But there are also young people with presbyopic. So judging a man whether he would need to wearing bifocals from the age is not scientific.