According to Telephia:
European Teenagers (15-17 yrs)purchase a new phone on average every 20 months, with 39% of teens purchasing at the one year mark. European young adults age 18-24 follow closely, buying new devices after 21 months. 35% of 18-24 year olds buy at the one year timeframe. On the other end of the spectrum, older mobile users age 55 and over keep their cell phones an average of two and half years, with new purchases usually occurring around 31 months.