Is this useful for individuals also? I would really like to know the optimal time to sell my car. Or is this more like chart analysis which only works as long as the people having access to that information is limited?

Theoretically it could be, but most fleets gather much more data about their vehicles than an average consumer. For example all repairs, parts and labor costs, maintenance, mileage, engine hours and much much more. In addition, majority now leverage telematics which greatly improves the resolution and depth of this data. This data is quite necessary to make our model work. From high level perspective though most consumers sell their vehicles way before that optimal time frame.