you shouldn't limit yourself. i shouldn't be the one pointing this out since i haven't ran a marathon. yet? this dude was 5'7" and ran it in 2:26 in 1935. https://en.m.wikipedia.org/wiki/Sohn_Kee-chung

i started running in my later years and ran my 2nd half last year. it's a great feeling to know how to run and am still learning.