Complex sentence: Mathematically, very few people born in the 20th century have yet had an opportunity to reach or surpass the age of 110, the age recognized by longevity researchers as the marker of supercentenarian status.
Split into simpler sentences: Mathematically, very few people born in the 20th century have yet had an opportunity to reach or surpass the age of 110. This is the age recognized by longevity researchers as the marker of supercentenarian status.