if he be and subjunctive mood

A man may live a very intense life if he be passionately devoted to
field-sports or beetles.

I am guessing the if he be passionately devoted to field-sports or beetles. is a subjunctive clause, because it is finite yet tenseless. And it seems that if someone be and be someone only work with be. Mandative subjunctive, it’s vital that someone do something, works with lots of verbs.
My questions is, is if someone be a vestige of old English, or is it something totally different?