Former President John Tyler’s (1790-1862) grandchildren still alive

Former President John Tyler, born 221 years ago, still has two living grandchildren. The one-term president isn't a well-known historical figure; he's probably best remembered for helping to push through the annexation of Texas in 1845, shortly before leaving office. So, how is it possible that a former president who died 150 years ago would still have direct descendents alive today? As it turns out, the Tyler men were known for fathering children late in life. And that math is pretty outstanding when added up:
John Tyler was born in 1790. He became the 10th president of the United States in 1841 after William Henry Harrison died in office. Tyler fathered Lyon Gardiner Tyler in 1853, at age 63.  Then, at the age of 71, Lyon Gardiner Tyler fathered Lyon Gardiner Tyler Jr. in 1924 and four years later at age 75, Harrison Ruffin Tyler. Both men are still alive today.
That means just three generations of the Tyler family are spread out over more than 200 years. President Tyler was also a prolific father, having 15 children (8 boys and 7 girls) with two wives.
He even allegedly fathered a child, John Dunjee, with one of his slaves.
Some context on Tyler's progeny: Jane Garfield (granddaughter of James Garfield) is 99, making her the oldest living grandchild of a former president, even though Garfield took office 40 years after Tyler.
Former Ambassador John Eisenhower is the oldest living presidential child, turning 89 this past August.
A few other Tyler tidbits:

• He joined the South's secession efforts shortly before his death and was even elected to the Confederate House of Representatives.
• Because of his Confederate ties, Tyler's is the only presidential death not officially mourned.
• Tyler ascended to the presidency in 1841. Other things that happened that year: Canada became a nation; the United States Senate has its first filibuster, lasting nearly a month; the city of Dallas, Texas was founded.