I'm a fairly senior mobile/web dev (12 years full time, part time and hobbyist before) and the best part of my job is mentoring the juniors! I push hard for hiring people who are hungry and fun to work with, and it's paid my company dividends. You can spend a few months training a junior or a twice the time hiring a senior, and the juniors always bring good energy and open minds. It's not for every company but I have enjoyed it immensely.