Well, I double-checked and yes, I think you should be able to change the ages by changing the labels, and the base fertility rates by changing the BCON values. But if you didn't have my aging mod in (or if you were using a different aging mod) while you got those numbers, then... they look correct, actually. Sims under 64 days old have a base autonomous pregnancy chance of 51%, and your 55-day elders could've had other modifiers (wants, aspiration, family size, being married) increasing those odds.