We have developed a technique to diagnose the stratospheric age spectrum and estimate the mean age of air using the distributions of at least four constituents with different photochemical lifetimes. We demonstrate the technique using a 3-D CTM and then apply the technique to OMS tropical balloon observations, UARS CLAES January 1993, and ACE February--March 2005 observations of CFC11, CFC12, CH4, and N2O. Our results using the ACE and OMS data are generally in agreement with mean age of air estimates from the chemical model and from observations of SF6 and CO2; however, the UARS-derived mean age estimates show an intrusion of very young tropical air into the midlatitude stratosphere. The UARS CLAES values of F11 and F12 appear to be significantly higher than ACE and model values and bias our lower-stratospheric estimates of the age derived from UARS data toward younger values.