I side with 22KR on the age thing.
As for the shoes - there are many factors involved, the quality/type of shoes, your running (some people are harder on their shoes than others), the conditions (trail vs pavement) and so on. But as an indication, I can usually go up to 800 kilometers on training shoes (and I use light shoes mostly, such as the NB 331 or Asics DS Trainer VIII). It helps to rotate your shoes if your run on consecutive days (i.e. have two pairs handy and ready to go...)
One last thing: welcome to this BB. As an introductory gift I'll explain the SMP Numero Uno Rule: you have to mention if your want "Serious replies only", otherwise you might end up with replies from the likes of Ed G, Run 42, Dave, Dr. Z, Zeke or me. :-)))))
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