I don't know if the childbearing age has been extended in the era of TNG, but it seems rather probable.
Though men are less and less likely to conceive as they grow old, it is relatively common for men to become fathers in their sixties, and the oldest recorded fathers were in their nineties, and even allegedly a father over 100.
Thus there seems to be little need to extend the maximum possible age of human fatherhood to explain occasional older fathers in Star Trek.
Women lose the ability to conceive children at a much younger age.
According to Memory Alpha, Kirayoshi O'Brien, son of Miles and Keiko, was born in 2373 during the DS9 episode "The Begotten".
His older sister Molly was born in 2368 in the TNG episode "Disaster" around stardate 45156.1.
In the DS9 episode "Dax", stardate 46910.1, Miles and Keiko went to Earth to visit Keiko's mother for her 100th birthday.
In 2373, in the DS9 episode "The Darkness and the Light", stardate 50416.2, Keiko and Molly visited Keiko's parents on Earth.
Since Keiko's mother was born in 2269 and Molly was born in 2368, 99 years later, and half of 99 is 49.5, Keiko would have been born about 2318 or 2319 if she and her mother became parents at the same age.
This is comparable to the medieval Princess Agnes of the Holy Roman Empire who was born in 1072 to 1073 and gave birth to her youngest (and at least 22nd) child Gertrude in about 1118 aged about 45 or 46. Though Gertrude is said to have died age 30 in 1150, thus making her born in 1119 to 1120 and Agnes about 46 to 48.
This is also somewhat similar to Maria Dobroniega, princess of Kiev, who married Duke Casimir I the Restorer of Poland and who youngest child Swietoslawa, Queen of Bohemia, was born about 1046 or 1048. Maria Dobroniega was supposedly born after 1012.
Maria Dobroniega was the daughter of Saint Vladimir I the Great of Kievian Rus but it is unknown which of Vladimir's known and suspected wives and mistresses was her mother.
The most interesting possible mother of Maria Dobroniega would be Anna Porphyrogenita (3 March 963-1008/11 or 1022), daughter of Byzantine Emperor Romanus II. She was born 83 to 85 years before her possible granddaughter Swietoslawa, so Maria Dobroniega would have been born about 1004 to 1006 if she gave birth to Swietoslawa at the same age - 41 to 43 - as her (possible) mother gave birth to her. If Anna gave birth to Maria Dobroniega around 1012 she would have been about 49 at the time.
Since Keiko's mother was born in 2269 and Kirayoshi was born in 2373, 104 years later, and half of 104 is 52, Keiko would have been born about 2321 if she and her mother became parents at the same age.
This would be comparable to the medieval Joanna of Pfirt, Duchess of Austria, who died in November 1351 after giving birth to her youngest child Duke Leopold III. Joanna was supposedly born in 1300.
But memory Alpha says this about Keiko's mother:
It's also interesting to note that Keiko's mother was apparently around the age of 60 when she had Keiko (assuming Keiko was not much older than 40 in 2369).
Rosalind Chao was born 23 September 1957, and so was aged 35 years, 4 months, and 26 days on 14 February 1993 when "Dax" aired for the first time, and a bit younger when her scenes were filmed. Unless Keiko is older than Rosalind Chao (which is possible) Keiko's mother would be almost 65 years older than Keiko.
The oldest women who have given birth to children conceived naturally include
Ruth Ann Kistler age 57 years, 4 months, and 7 days in 1956 (used hormone replacement therapy).
Mrs. George Saunders age 58, 1818.
Dawn Brooke 59 years. August 1997 (used hormone replacement therapy).
All older mothers, up to the age of 70 or 72, and many younger mothers, have used in vitro fertilization to conceive.
Thus it is seems probable that Keiko's mother gave birth to Keiko at an extremely old - though not record breaking - age by our standards. This may be due to 24th century medicine delaying her menopause for a number of years or to her use of in vitro fertilization, or to some other medical factor I have not thought of.