Don't worry about size! She'll probably insist on calling the shots until he is old enough, but that is a dominance and not an acceptance issue and you have to let them work it out between them. Acceptance happens before the dominance phase.
If there is mutual interest, I would think that you are in with a very good chance. I would keep piggies with severe teeth chattering and other signs of major aggression that can lead up to a bloody fight away from each other as things will probably not work out at that time; as I say, a minor bout during intro can happen when boar goes overboard and girl has to be a bit more forceful in telling him off. But that usually happens after the initial acceptance and is much milder in intensity. A sow that goes straight for a boar as soon as he tries it on won't bond.
The sows who won't accept a boar are mostly dominant older sows past ideal pup bearing age or some ex breeder sows who must have had a really bad time having been thrown together with several boars at the same time. Most girls up to two years and non dominant older sows have no problems with a boar.
The age of a boar is irrelevant. My first sow/neutered boar bond was between 3 1/2 year old Dizzy and 12 month old Llewelyn, and they simply adored each other. She would insist on teaching him proper manners, though!