Lines and wrinkles are caused by a number of factors, such as:

Natural ageing
Sun exposure, and long-term UV exposure, can result in reduced skin elasticity and degradation of skin texture. When our skin is exposed to the sun, it is damaged and this can cause fine lines.
Smoking can accelerate the normal ageing process of your skin, contributing to wrinkles. This may be due to changes in the blood supply to your skin.
Repeated facial expressions such as frowning, smiling or lifting the forehead muscles in surprise. Wrinkles are likely to form and set in those locations.