Ah the injuries, that'll do it for you.
I was doing the same in my late 30s, although not those times - 4 runs a week, half marathon long run practically every week.
Then an injury in late 2012 training for 'Britain's toughest 10K' - a nice hilly race that takes place on New Years Day.
I finally entered that in 2016, 3 years after, that's how long it took me to get over that particular injury.
Never the same after though.