Thanks for asking me to reply. Flat feet at your age is less amenable to correction. You can wear shoes with medial arch support. You can order one with the orthotist won you can find at your local physio clinic. It's a matter of practice. Start with running small distances and join a local group. You will surprised to find the number of runners with flat feet. Eat green leafy vegetables and fresh fruits and sleep for 7-8 hours daily to keep up your stamina for the whole day. Good luck.