Maggie Taylor and May O'Neill joined their family for a birthday bash in Magherafelt, enjoying the day with their four children, 13 grandchildren and 11 great-grandchildren.
It might have been a belated celebration, as Mary was under the weather for their actual birthday in May, but they were delighted nonetheless.
"They're always very witty, enjoy company, enjoy life," Maggie's son John told UTV.
"They like a game of bingo, like partying, they like a day at the seaside. They never grew old - they always stayed young."
I'm hoping I'll see 100 and that'll be a bigger celebration!
Maggie is the oldest by just half an hour and even their parents had trouble telling them apart. They've always lived near each other and have been the best of friends all their lives.
The ladies put their long life down to a good breakfast of porridge, no smoking or drinking, and no powder or paint as they call it.
Magherafelt can also boast the tallest twins in the UK - the Knipe brothers born in the town in 1761 and both measuring 7ft 2ins.