A lot of kilometres: 526,254 km, about 1.3 times what a 26-year-old car usually has. Ask for the service history, and when the timing belt and clutch were last done.
An older car: 26 years old. Cars over ten years need an NCT every year, and repairs and parts weigh more in what it costs to keep.
The NCT ran out in March 2024. Ask whether it has been tested since.