Not at all. Around 12,000 miles a year is considered average, so anything below 120,000 miles on a 10-year-old car is below average. If anything, the mileage could be too low. A diesel Golf of this age will have a diesel particulate filter (DPF). If it's mainly been used for short journeys, this could be clogged which will cause expensive issues. You might be better looking for a diesel Golf with a higher mileage or a petrol model.