Actually, many WWI veterans flew again in Spain and WWII. Though I have no details on the personel of the Legion Condor (correct sequence), I do know that Von Schleich was the leader of JG26 in the first months of WWII, until replaced by Handrick. Others also served as leaders, notably Osterkamp who was in charge of JG? until he was put in charge of all fighter operations against England in 1940. Most JG's were originally lead by famous WWI veterans as it was thought their combat record and personality would invigorate their pilots. It worked for a while until it became obvious that the new war was different in so much that the older veterans -well in their forties- had to be retired from active command. They went to higher offices, in administrative duties or inspectorates.
There were many many more but their names escape me now. The ones that I do remember (not necessarily in a fighter establishment) are:
Dr.Erich Mix,
Harry von Bülow-Bothkamp, Josef Veltjens (KIA) and
Karl Thom (MIA).
Most WWI airveterans of repute who were still alive when WWII began, saw service with the Luftwaffe, attaining ranks between Major and diverse classes of general. Some joined the Luftwaffe as early as its inception and were instrumental in rebuilding the German air force.
On Condor Legion veterans I must remain silent however.
Kind regards,
Reinout