I run up to 30 miles a week, in summer mainly trail. I am male and 72 years old and thank God have no issues with knees, shins or any other body parts. I always want to increase my speed but no fartlek, tempo or whatever is good for me because I have absolutely no concept of pace - I haven't a clue about my speed at any given time. I start off fairly fast and as I tire I slow down, ( I think). I'm quite happy in my running, should I just continue as I am?