My wakeup HR hasn't risen much as I've gotten older

I normally would have run this morning, but my wife and I are leaving for an early morning church activity, and we'll go directly to our work. I'll run tomorrow. My wakeup HR this morning was 52. When I started running marathons about 22 years ago, my wake up HR was 44. After my first year of marathons (two marathons that year) my HR dropped to 40 and remained there during the next year (two more marathons). So, after 20 years of short distance running, my HR is still pretty low for an old guy my age.