A domain never loses it's age.. Even if it changes owners 10 times. Page rank can be lost, which is quite common. But, if you can post fresh content and build backlinks again, it might stay.
are you sure about the domain not losing its age? expiring domains like these aren't just changing owners, they're being registered as a brand new domain, so the whois record would show the registration date as 4-Jan-2012 rather than the original registration date.
as for page rank, when i've registered expired domains in the past, the page rank usually drops to 0 or N/A in the next PR update, but regains it's PR in the update after that.