The best way to prevent premature ageing is to limit your time in the sun, particularly between 10am and 2pm when the sun’s rays are most harmful or 11am and 3pm during daylight savings.
When you are outside, wear a hat and apply a broad spectrum SPF 30+ sunscreen to all exposed areas. Sunscreens need to be applied liberally at least 15 minutes before going out in the sun and should be reapplied every 2 hours and after swimming or exercise.
Protection is necessary even on cloudy days, since up to 80% of UV rays can penetrate light cloud cover. So it’s important to use sunscreen all year round, particularly on your face.