Obviously not just a Leeds Bradford thing then. On reflection, we only saw JAT 707s at LBA for one season, thereafter being supplanted by the 727 on the Pula flights. By this time JAT had a few new 737-300s, thereby releasing a few DC9s and 727s for the Yugotours work and perhaps relegating the 707s further !
At the time I thought the 707s were a pair of old bangers, apart from being proper old aeroplanes. Yet they were only about twenty years old when they passed through LBA. Now Jet2 has at least one thirty year-old 737 in its fleet !