When I was young, and unmarried, I changed cars every 7-8 years on average. I thought I was doing pretty well! Some of my friends got new upgrades every 2-3 years!
Then I got married and had kids and realized there are far more important things to spend money on, including savings.
So we now keep our cars around 15 years.
To the bolded that would be my in-laws including my sisters-in-laws.
I've known my husband for 9 years (next month). In that time here's the cars they have had in the order that they have had them:
~Step-father-in-law: Tundra, F150, F150 [current] and they just ordered a custom F350 but will be trading in the current F150 (one already listed)
~Mother-in-law: Corolla, Infiniti (can't remember the model), Explorer, inherited her mom's Camry (still have), just bought 2001 Explorer for commuter car since they don't want to drive the F350 around every day
~Sister-in-law: scion tc (totaled), older jeep, eclipse, cadillac (can't remember the model had recall problems never worked quite right), traded prior cadillac for a newer year same model (now having problems with it)
~Other sister-in-law: scion TC limited edition one (leased but paid in full and then traded in before lease was up), at least 6 cars (all used and in pretty iffy shape including current one don't remember model as she's had so many cars)
~My husband: scion tc (traded in with infiniti so him mom could get explorer and he got the corolla for a few months), mazda 3 [current] (traded in corolla to help with mazda 3). I never agreed with him turning in his scion tc because he would have owned that car years ago instead of having a car payment for forever (aside from the corolla that he didn't have to pay for for the few months that he had it) but his mom pressured him to turn it in to help with her getting the infiniti
Unless otherwise noted all vehicles were bought brand new (i.e. $$)
To be fair the in-laws say they have always purchased/traded cars within 2 or 3 years. Step-father-in-law was a car salesmen for a few years before switching to being an insurance agent.
Growing up my dad always leased cars with the exception of a handful bought overtime over his lifetime.
In the time I have known them I have had 1 car and its the first car I have ever owned (see my above comment).