Aage I Petersen is not mentioned in Malcolm's fine Air of Authority www.rafweb.org RAF Casualties lists for either 1918, 1919 or 1920.
Nor (if you've not checked yet) does he appear in the CWGC War Dead db.
As far as I can see, there is no AI Petersen in either the May 1918 nor Aug 1919 Air Force List - CDs again courtesy of Air of Authority.
However, there is an A Petersen in the March 1919 Air Force List which might be him:
p205 Col 725a, Observer 2nd Lt A Petersen 22 Jul 1918
(National Library of Scotland Military Lists archive)
Perhaps one of the WW I forums might help?
You may recall that a number of WW I airmen survived the war, only to die in RAF service during the 1919 Influenza epidemic...
best wishes with this one