I currently drive a Suzuki Splash which is 8 years old and worth less than £2,000 according to Parker’s guide. The Alto, smaller than the Splash, was one of the cheapest cars on sale when I bought my Suzuki so I would pay a lot for one that is 16 years old, although the low mileage is a bonus.
It depends what you want from a car. If you are planning to keep it for a few years then I would not buy one that is 16 years old whatever the price. If you only need it for a few months then it might be fine but be prepared to spend money on new parts such as battery, brake pads, exhaust, tyres etc. Check any promises made by the garage, so they do a pre sale list of any checks they have done or any warranties they offer.
Above all, go online to check the price, if you know the registration number or year and model it will be easy to get a guide price.