Have you ever completed a marathon 26.2 mile run?

[krafty89]

I'd take inspiration from many "older" runners that have taken up running, i'm sure you'll be able to find all sorts of runners that have taken it up and decided to do Marathons.
The 40mins for 10k is a very good target, my Dad (Who is 58 by the way) started running 8 years ago and has improved his 10k time from 43:30 to 37:30 which was set this year!
Good luck!