Scrapping age is 15 years. However I did get a plane back from a bankrupt leasee and it was in such bad shape the system let me scrap it early (off topic, but think this discussed elsewhere and a great enhancement).
I think what would make sense is for the first generation jets to have a lower scrap age if that is feasible to program. For example, maybe the Caravelles I, II, III, the Early Comets, first 707s, DC8 -10/20 could be 8 years as these are almost obsolete by the first D check. That way-theoretically-you wouldn't have 2 pages of DC-8-10 & 20s to scroll through if folks actually scrapped them.
Maybe the next gen planes like the HS 1C, Caravelle N, Dc-8 30/40. are set at 10-12 years. Then I'd think 15 years is reasonable for the planes that come out by the late 1960s and have reasonable operating costs.
Not sure about the 737-100 and 727-100, could fall in 10-12 years, but realistically real airlines flew these things close to 25-30 years. united was flying their 727-100s well into 1990s and I flew a Continetal 737-100 originally delivered to Lufthansa in 1990s and it had a back left door that was actually stairs that folded up into the cabin
. I think delta is still flying a few remaining 40+ year old NW DC-9s...although not advocating that.