Well, maybe their systems needed priming, and are now primed and ready!

If they're fit enough to grow, birth and feed lambs, and you don't mind managing unseasonable lambs if it happens, and really want to give it a go, then go ahead. But if you think that either of them would or might struggle, then sorry but it wouldn't be a risk I would take.
The oldest lambing ewe I have heard of was a 17 year old Herdwick. She lambed and successfully reared a single lamb out on the Lakeland fells every year bar 1 from her 4th to her 17th. (The shepherd liked them to mature slowly, they had their first lamb at 4.)