To answer Safrane's point:
The average year of full leather cars for sale in Feb'15 was 2005.4, in Apr '16 it was 2006.3. BUT the average year of cars for sale was 2006.4 last August and it was 2006.3 in April this year, so no real change in average age. And over that period full leather cars saw prices increase by 9.1% (if you look at the chart, prices bounced around early late year and then the real rise started in the summer). So the data suggests that age has not been a factor.
The average year of full leather cars for sale in Feb'15 was 2005.4, in Apr '16 it was 2006.3. BUT the average year of cars for sale was 2006.4 last August and it was 2006.3 in April this year, so no real change in average age. And over that period full leather cars saw prices increase by 9.1% (if you look at the chart, prices bounced around early late year and then the real rise started in the summer). So the data suggests that age has not been a factor.