What a difference a couple of decades makes
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Since starting to run at least one marathon a year in 1977 at age 34 just for the heck of it to see if being in good shape anyway from winter skiing, etc. was good enough to run 26.2 miles, without that much, if any, training, it’s worked out to run the Seattle Marathon 15 times since 1990.
 
For the first 25 years from 1977 - 2001, it was possible to slip under four hours every once in a while in annual marathons without that much trouble. The first marathon over five hours wasn’t until I tried a test of running 26.2 miles in March 2003 only drinking water and nothing else.  It was supposed to make me strong for a summer Ironman.  It didn’t work. 
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However, within just six years - 2009, even all the nutrition I could stand couldn’t stop Father Time from turning me into the permanent five hour marathoner that I once vowed would make me quit running marathons altogether. Now, this year for the first time, my beloved SM has taken more than six hours.
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Oddly enough, even though 26.2 miles now takes more than six hours, I’m still running all the way. It’s just that a prematurely old right knee has abbreviated the longer strides of old so it now takes 60,000 and more steps to run 26.2 miles instead of only 46,000 in those days. (By comparison, I think marathon elites only need 20-25,000 steps).
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Everyone starts slowing down at different ages and rates but it still surprises me how much I’ve slowed down in recent years, especially compared to other runner friends.

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•MegaBob (MM#32 - 83 yo / 500+ marathons) ran sub-fours through age 77 and sub-five hours until age 80.

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• Magnificent Mel (MM#24 - 79 yo) was doing five’s at ease until last year’s fall off a ladder and the full-body cast broken back his doctors mistakenly thought would end his running career at age 78. 
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• Keith Wood (83) ran 4:36:31 in this fall’s edition of the Tunnel Lite Marathon.

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• my now 82-yo Ironman mentor friend is finally taking more than five hours for marathons even though he never runs for more than two hours in his year-round training and all of his marathons are after the 2.4 miles of swimming and 112 cycling.

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• still slim and trim as ever, my former nemesis Vegan Judy (MM#162 / also 69) and I had been beating each other back-and-forth for more two decades ever since my 4:06:59 and her 4:14:13 in the 1990 Goodwill Games Marathon (at 97 degrees). However, she continues to get faster, very much faster, with getting older, e.g. 3:58:53 in this summer’s famed Light-at-the-end-of-the-Tunnel Marathon.

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I can’t help myself from longing for those days of running together when I realize how far ahead of me they are now. However, the marathon distance hasn’t changed and I’m grateful to still be looking forward, year-after-year, with renewed anticipation to its various challenges, . .to say nothing of many new friends from the back-of-the-pack too.   
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Doesn’t matter though as, compared to the four hour cutoff in some marathons in those days (and the humiliation  fitness runners suffered by being that slow), generous, if any, cutoff times nowadays plus early and super-early, . . . we call ‘em remedial, starts provide ample opportunities for 26.2 miles of good exercise almost any weekend that’s convenient, usually with increasing numbers of other, like-minded, similarly-slow, fitness and fun runners of all ages.  Sure makes me glad I didn’t quit running when I said I would.
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Now if I could just be like Judy and get back to our 1990 weights too . . . .

Sort of figured there had to be one

You're comparing yourself to some pretty elite company there!  But take a step back to see the bigger picture and you're way out on the front edge  of the bell curve.  Keep doing it for fun and enjoy the ride.

Tramps has it right.  Your comparison group is not, ahem, representative of the population.  Put anybody on this forum in a marathon with the "right" 1,000 competitors in it and our dear RA friend will come in dead last.  Conversely, if I were to randomly grab from the street 1,000 competitors your age I would bet you come in first.  All I can say is that I hope to one day replicate your having run as long as you have.  In my book you have won all there is for us to win.

Its never too late to try new tricks!  You could always break your tradition of not training........