The AA says that 9000 miles per year is the average for domestic use.
Think carefully about the diesel car - they are economic for high mileage useage, less so for low mileage.
However, diesel engines do tend to have a much longer life that petrol, and even 90,000 miles would not be considered 'high mileage' for a diesel car.
Mileage is not the only consideration - it would be better to have a higher mileage car that has been well maintained and looked after than a lower mileage car that has been run into the ground without proper servicing.
My car is a year 2000, and has done less than 20,000. That is exceptionally low. For a petrol car, over 90000 would be considered high.