In college, I had one bass, and gigged weekly. I changed strings every 6 months or so, because that's all I could afford. Now, I have a small herd of basses, I gig weekly (and practice a lot more than I ever did in college), and I change strings...about every 9 months., but that's changing al the strings on all the basses every 9 months. I keep track of when I change strings - the data as to how long sets last helps me be wise with string purchases.
Although I used to change strings "more often", that's misleading. College was a while ago, and all the lights were incandescent back then - stages were really hot, and I sweated a LOT, for 3 hours, twice a week.. My strings were drenched in sweat every gig. Nowadays, all the lights are LED's. and the fixtures are much further way - stages are cool nowadays, I don't sweat at all, and I do church gigs - 2 half hour sets a week (and 15 to 20 hours of practice). So, the strings I would change in college were much "older" - more dead than the ones I change nowadays, even though the ones I change now have more hours on them.