According to his Pottermore profile1, Tom Marvolo Riddle was born on 31 December, 1926. This means he would have been nearing his 55th birthday on the night he failed to kill Harry, and nearly 72 by the time of his death2.
He's firmly in the generation of Harry's grandparents.
That being said, Voldemort certainly wasn't the originator of his particular brand of vitriol; the notion of pureblood supremacy over muggles (and muggle-borns) is much older than him, and goes back at least as far as Salazar Slytherin:
The term 'pure-blood' refers to a family or individual without Muggle (non-magic) blood. The concept is generally associated with Salazar Slytherin, one of the four founders of Hogwarts School of Witchcraft and Wizardry, whose aversion to teaching anybody of Muggle parentage eventually led to a breach with his three fellow founders, and his resignation from the school.
According to the Pottermore article on "pure-bloodedness" (also the source of the above quote), the anti-Muggle-born sentiment started to gain serious traction in 1692, with the introduction of the Statute of Wizarding Secrecy:
Magical opinion underwent something of a shift after the International Statute of Secrecy became effective in 1692, when the magical community went into voluntary hiding following persecution by Muggles.
Under such conditions of uncertainty, fear and resentment, the pure-blood doctrine began to gain followers. As a general rule, those who adopted it were also those who had most strenuously opposed the International Statute of Secrecy, advocating instead outright war on the Muggles. Increasing numbers of wizards now preached that marriage with a Muggle did not merely risk a possible breach of the new Statute, but that it was shameful, unnatural and would lead to 'contamination' of magical blood.
1 If you're not a fan of Pottermore (and who can blame you) we can ballpark his age by recalling that Tom was a prefect when Hagrid was expelled for (allegedly) opening the Chamber of Secrets, fifty years before 1992 - Harry's second year. So Tom would have been 15-17 in c. 1942, which puts his birth year c. 1925-1927.
2 In calendar years, anyway; his actual physical age is difficult to determine, because of the whole "resurrection" thing