Positron annihilation age momentum correlation (AMOC) experiments were performed in linear and in cross-linked poly(metha methyl acrylate), PMMA at low and high temperatures. The lifetime spectra and doppler broadened lineshape S(t) data were analyzed with Byakov and Stepanov's blob model for the formation of positronium. We found that the analysis is consistent with a delayed formation of positronium and also offers an alternative explanation for the observed broadening of the annihilation radiation lineshape at short times (a few tens of ps) after positron injection, the so called young age broadening.