The Daily Mail has an interesting article on President John Tyler's two grandsons, who are still alive despite the fact that Tyler was born in 1790. (ht) Normally I would trust the Daily Mail about as far as I can throw the British Isles, but confirmation for this is easy to find, and they have the handiest article of it, complete with pictures and family tree. Basically the timeline is:
1790 John Tyler was born
1841 Tyler becomes Vice President and then becomes President on the death of William Henry Harrison
1844 Tyler marries Julia Gardiner Tyler, his second wife, who was thirty years his junior
1853 Lyon Gardiner Tyler born
1923 Lyon Gardiner Tyler marries Sue Ruffin, his second wife, who was twenty-six years his junior
1925 Lyon Gardiner Tyler, Jr. born
1928 Harrison Ruffin Tyler born
1935 Lyon Gardiner Tyler, Sr. dies
And Lyon Gardiner Tyler, Jr. and Harrison Ruffin Tyler are both still alive; their grandfather had started his political career on the eve of the War of 1812.