The problem is that you said you're not athletic or not a conditioned athlete, then described exactly what it takes to become a conditioned athletic person - dedication to training and putting in the mileage.
Anyone that can run a half marathon every weekend and 30km+ during the week is almost by definition athletic. Yes, nearly anyone can achieve this with the dedication it takes, but that doesn't change the fact you're being overly humble about your own athleticism.
It's like someone saying "I'm not an engineer, and am not particularly good at math or physics, but I studied 3 days a week and got an engineering degree and now I work at an engineering firm and can solve most math and physics problems."
Anyone that can run a half marathon every weekend and 30km+ during the week is almost by definition athletic. Yes, nearly anyone can achieve this with the dedication it takes, but that doesn't change the fact you're being overly humble about your own athleticism.
It's like someone saying "I'm not an engineer, and am not particularly good at math or physics, but I studied 3 days a week and got an engineering degree and now I work at an engineering firm and can solve most math and physics problems."