Oldest Squadron
No 1 Squadron RFC did indeed begin with balloons, but was flying fixed-wing aircraft by 1914.
The first fixed-wing squadrons in the RFC were Nos. II and 3, today flying Tornado GR4s and Typhoon F2s, respectively.
From the RAF Marham website:
No II Squadron Royal Flying Corps, was formed on 13 May 1912 at Farnborough just one month after the Royal Flying Corps itself was created. The Squadron, along with No 3 Squadron, had the distinction of being the first fixed-wing flying squadrons to be created in the world (No 1 Squadron flew balloons), thus the precedence was set for II (AC) Squadron to establish a number of firsts throughout its history.
JT