My 16 year old son wants to walk 72km in a single day.

My 16 year old son recently bought a Fitbit and has strived to continually bolster his goal of daily walking. Recently he came to me and proposed that he would like to do 100,000 steps in one day. I didn't realise at the time this would be such a massive distance, and as he has become more serious about his proposition he told me it would be around 72km. The past week or so he has been doing around 20 kilometres on days to prepare himself, but it will be a massive leap from his preparation to the actual day. He believes that this will take him over 14 hours and that his route would be repeating a loop around 10km long. I'm not entirely sure what to do in this situation. Of course, walking is great for his health and I'm incredibly happy that he's being active, but at the same time I don't want him to do any permanent damage. He is definitely fit and active and often does running middle distance as well as lots of sport. What do others think? And is there anything important I may have missed? via /r/Parenting http://ift.tt/2cK95fI