Somewhere in Time - Who is this character?

In the time-travel romance movie "Somewhere in Time", a young playwright from 1972 uses an old pocket-watch to mystically travel back to 1912 and meet an actress he has fallen in love with from old photos. The film has a paradox where:

When he gets to 1912, the actress' manager is a middle-aged man (portrayed by Christopher Plummer) who is not only super-protective of her, but also told her that she would meet a young man and fall in love. Throughout the film, the manager than tries to keep them apart, supposedly for the woman's "own good".

I remember when watching this originally, I expected the manager to be an older version of the playwright character who was trying to change his OWN past. However, that can't be since

So, my question is WHO is the manager (really) and HOW did he know what was going to happen in the (relative to 1912) near future?