We just got into pigs a year ago but we have found that waiting till the sow comes in heat and then putting them together just to let them breed works well. You have to put them together a few times this way so its a bit more work, but than you know when she is bred and know when to expect your piglets. You can keep them together as well but make sure they don't get to rough with each other. Also if the boar is that much older make sure he isn't to big for your sow cuz she might not be able to hold him up.
They ended up being not to different in size she about half his size. And thankfully he acts like a gentlemen. I didn't expect them to be as big as they are. He a good solid 500-600 pounds and she a good 250-300 pounds. He comes up to my hip he is massive and she isn't much shorter he might have an inch or two on her but that it. He long where she short bodied. He the one in the back and the one in the picture by himself.
Also this pen is very much temporary the other pen I set up would not have held them according to my husband the fencing (cattle pannel and horse wire wasn't strong enough. Plus no clue how we would have walked them in to it past my garden. It took two hours to get the female off the trailer the boar just jumped off and was happy. I have to say so far I like him better then her. However he did get between me and her protecting her when I was watering them. I will say I have never dealt with pigs so it's very new to me and I am being extra careful around them while trying to be friendly with them.