If you read the posting more closely you'll notice that they say they are putting a panel together and it's headed under Future Recruitment. So from that point of view goodness knows when training or actual recruitment would start. Pals of mine in EI say there's meant to be a redundancy programme soon - to encourage longer serving staff to leave - but that could all be pie in the sky too.
I would imagine that LGW crew would be offered to transfer base if they wanted.
As for when they last recruited, they took on cabin crew last year for DUB and I don't think that they were all in their 20's. Some were in their 40's as far as I know.
As for ages there are a good few of them still in the their 20's. I know one who is 25. She started 5/6 years ago. But yes there are obviously crew in their 30's 40's and 50's - like many other 'former' national carriers/flag carriers.