I am trying to build two profiles separately describing the 8-year cars and 18-year cars. But when I change the "vintage year", all "vintage year" in all life profile also changed automatically.
I think 8-year cars have a vintage year of 8 and 18-year cars have a vintage year of 18. So how can I separately define the different vintage year here?
Unfortunately, it is not possible to define different vintage years across different lifecycle profiles. I suggest changing the 8-year Vehicle Survival Profile so that the values from Year 9 to Year 18 are equal to 0%. This means that no cars will survive after the 8th year.
What you have done with the Stock Profile/Vintage Profile is correct, by leaving it at 0% after Year 8.