Longitudinal Assessment of the Effect of Age and Experience on Performance in 161-km Ultramarathons An American study examined at 4,066 runners with their 29'311 competitions from 1974-2010 the influence of age on the mileage at 100-mile runs. By the age of 38, men like women were slower at 0.05-06 h / year. Between 38 and 50 years, men were slower 0.17 h / year, the women 0.23 h / year.
If the number of feminished runs were examined so were men with 10 and more dinished runs 1.3h faster, women 1.7 h faster and the fastest men harb 3 h faster. The interesting numbers can be found under https://pubmed.ncbi.nlm.nih.gov/24910926/