peaks in the late teens to late 20s, declines noticeably after 30, and drops rapidly after 35, making pregnancy less likely and increasing risks like miscarriage or chromosomal issues, with natural conception very rare by 45, though modern medicine allows births well into the 50s (often with donor eggs). Men's fertility also declines with age, though less predictably. Fertility & Age: The Decline Peak Fertility (Late Teens - Late 20s): Highest chance of conception and lowest risk of complication