Pilot flying...
According to the first report from the BEA, it says that:
"The airline’s procedures(5) specify that to be a replacement duty pilot, a crew member must have the same rating as the crew member that he or she is replacing and, in addition, during the captain’s rest period, a pilot with the same license as the captain must be at the controls."
This tells me that 37yo F/O had to be at the controls because the 32yo F/O did not have the same license so was not qualified (according to AF procedures) to be PF while Captain was on rest break.
However, we can't be certain which seat he might have been flying from. Either of the two were qualified to be flying the plane with the Captain in the LC.
So, if the 37yo took off in the right chair, he would probably have still been there flying the plane at the time of the incident. If he was the Captain's relief, he was probably flying from the left chair with the 32yo in the right where he'd been since leaving Rio.