When Tom Riddle was a 6th year, Hagrid was a 3rd year. That's the year that Hagrid was expelled. Myrtle was alive until that year, also. Dumbledore was teaching Transfiguration, Horace Slughorn taught Potions, Armando Dippet was Headmaster, Galatea Merrythought was finishing up nearly 50 years of teaching Defense Against the Dark Arts.
A wizard named Nott was a student with him, who became a Death Eater eventually. Bellatrix's future father-in-law, Lestrange, was also a student and in the Slug Club. A student called Avery was also in the Slug Club and was one of the earliest Death Eaters. Avery would have a son, who would be a Death Eater closer to Snape's age.
The best place to get info about Tom Riddle in his early years is obviously Half-Blood Prince, through Slughorn's memory and Dumbledore's memory - and Chamber of Secrets.