Curiously the same thing happens with a rose chafer Cetonia aurata, the other side of the Atlantic, which is also sometimes seen at this time of the year. Our rose chafers emerge, officially, in the spring and mate soon afterwards, quite a bit earlier than June. So my guess is that even though they are tempted to come out in the autumn they will not be mating now; worth keeping an eye out for this though...
By the way, one should be able to tell if it is freshly emerged, the beetle will be covered with a lot more hairs, very aparent in this one...
Alas I can't sex them, wish that I could... Interesting covered scutellum, beautiful beetle, another jewel :-)