At the half-year mark in 2012, I reported that the aviation industry appeared to be headed toward another significant drop in the annual average age for commercial jet aircraft retirements, with potentially big implications for aircraft residual values, financing options, parts pricing, lease rates and more. At that point, Aviation Week's Fleet database showed the average age dipping below 25.

Now the full-year results are in, and the average age did not end up below 25. It ended up below 24.

Whether the precipitous 2012 decline is an anomaly or the confirmation of a downward trend will matter a lot, and 2013 is shaping up as the year that will tell the tale.

First, the numbers.

A retirement-age analysis using Aviation Week's Fleet database shows an average retirement age of 23.2 years in 2012, down from 26.6 in 2011 and the lowest level in more than two decades. Retirement figures could yet change for 2012—and even for some of the earlier years—as aircraft now classified as stored are reclassified as retired after years of sitting, or some long-sitting aircraft make their way back into the operating market. But that is not likely to make a big difference in the trend.

The fleet data as of Jan. 17 shows 477 aircraft retired in 2012—126 widebodies, 317 narrowbodies and 34 regional jets—and the decline in the average age was not attributable to just one grouping. The average declined to 24.8 from 27.5 for widebodies, to 23.5 from 26.9 for narrowbodies and to 14.2 from 17.8 for regional jets.

Within the groupings, however, there were clear contributors.