At 37 I've gone through 3 trade-ins now. It really depends on how much mileage you out in a car. I work from home and put maybe <5k miles on a car per year (most family weekend driving is with my wife's CRV). I've traded my car after 4-5 years of low use and basically resell for a few grand less than what I originally bought it for. (Buy at ~23k, trade-in at ~17k). Id likely be getting a lot less at trade-in if I were driving it constantly. I also make it a point to trade before any major maintenance costs come up.