[en] The mean age of air is a classical diagnostic of the transit time from the troposphere to the various regions of the stratosphere, providing insights on the strength and structure of the Brewer-Dobson Circulation (BDC), the polar vortex and the irreversible mixing in the mid-latitudes. We apply this diagnostic to the WACCM chemistry-climate model for the 1985-2014 period. A comparison is presented between unconstrained simulations (FR-WACCM) with and without the representation of the QBO, simulations nudged to the MERRA-2 reanalysis (SD-WACCM), in-situ measurements and a chemistry-transport model (CTM). The results are different depending on the simulation, with SD-WACCM resulting closer to the observations w.r.t. FR-WACCM. In the FR-WACCM the QBO plays a role leading to older age of air. The time evolution over the considered period is slightly decreasing, while observations show a positive (not significant) trend. Given those results, further studies have to be carried out investigating the multi-decadal trends of mean age of air and involving actual tracers.