My resting heart rate is 42. Has been for decades. I am 63. Exercising I have gotten up to a heart max of 163 on a heart rate monitor during all out intervals. Probably add two for what is true heart rate max.
My doctor is fine with my heart rate.
FWIW my regular exercise probably is not the cause; I exercise but I’m not doing half Ironmans lately. I think it is just familial high parasympathetic tone, a conclusion supported by the fact that one son also has a resting heart rate in the low 40s. (And does powerlifting more than endurance.)
Lower heart resting heart rate, 50s or less, is associated with greater longevity, and higher shorter life expectancy.
You should worry about a low heart rate if you are symptomatic with it. And a resting heart rate over 75 is an alarm bell.