Sorry, I can't help on their exact ages - but I think I'm right in saying they're not elderly by any means?
The phaseout is a weird one because EAZA have never been consistent on their decision - I think it was 2019 they decided to make them a phaseout species to focus on banteng, but in the same year gave them a new-style EEP and didn't make the phaseout actually official outside of the website and magazine releases. Last year Berlin gained a new breeding bull and I was told that they, logically, intended to breed (the keepers weren't aware of a phaseout at all, in fact). And that coincided with EAZA releasing new information on several cattle including gaur that had all mention of phaseout removed. Also worth mentioning that it had been a fairly pointless endeavour anyway - only Whipsnade actually stopped breeding them, and I believe it was Zlin that actually imported new stock from Asia. Given how prevalent banteng are and how easily they breed, it does seem logical to allow collections capable of holding gaur to breed them.