You can use the delayed entry function to restrict comparisons to 25-35 years: https://support.sas.com/documentation/onlinedoc/stat/ex_code/141/phrcpa1.html However, when you are using parity as the outcome, you should also account for pertinent competing risks (at least all-cause mortality): https://support.sas.com/rnd/app/stat/papers/2014/competingrisk2014.pdf
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