I made no mention of 35 I know that's base on very old French records and may well not be applicable to modern populations.
However - conception rates do drop with age
But women become less fertile as they get older. One study found that among couples having regular unprotected sex:
aged 19 to 26 – 92% will conceive after 1 year and 98% after 2 years
aged 35 to 39 – 82% will conceive after 1 year and 90% after 2 years
NHS
and miscarriage risks increase:
the risk of miscarriage was lowest in women aged 25-29 (10%), and rose rapidly after age 30, reaching 53% in women aged 45 and over. bmj
Despite that you can get people like DH GM who got pg and had healthy twins at 51 - it's just much rarer.
I've 45 - most women I know who really wanted children were trying at 40 as it does get harder for many to have successful pg - though science is improving the odds.
But fertility does decline with age - though I agree its not a cliff and I never said it was.