Olive oil does not improve with age. the flavours in olive oil begin to deteriorate after 12 months and the oil might become very bland and tasteless after 18 months.
If possible, choose oils from that have the year of harvest on the label. Ideally the label should also include the date of pressing. Many oils have a "best before" date, but this is not altogether helpful.

The colour of the oil is influenced by the degree of ripeness of the fruit when pressed, and also by the cultivar. Usually greener fruit produces a greener coloured oil. So don't let the colour of the oil influence your choice to much, although oil from a riper fruit (a pale golden colour) generally has a milder flavour.

Virgin extra oil keeps better in the dark, away from the heat and light. Try to buy oil in a dark bottle and away from a source where the oil is stored in a cool place away from direct light.
Supermarkets may be convenient, but the are not necessarily the best place to shop for extra virgin olive oil.

Price is not always an indicator of quality. Smart packaging, especially smart glass, is expensive and adds to the price of oil. When you find an oil to your taste, check to see whether you can buy it in a plastic container at a reduced price and bottle it into glass yourself when you get home. In fact, one of the best reasons for buying olive oil direct from the farms, is that the price is often lower than that in the stores.

If you are keen on flavoured olive oils, remember that these oils can no longer accurately be referred to as "extra virgin", because foreign elements have been introduced into the oil. You may need to check the quality of the oil as well - after all no one makes gluhwein from good quality wines!