Why Panic, check your PM.
If someone at Jetgo did send you such an email, you probably could go them
not only on age discrimination but for threats - even if they have no hope of carrying them out with any effect. You obviously need to take legal advice on the latter, but the former would appear clear cut enough.
I recall back at the time of the great pilot dispute of 89 a couple of hotheads touring flying schools making threats to the young hopefuls that if they took airline jobs from the old mates, these kids would be blacklisted forever. It was a pathetic and empty threat by a few very immature individuals.