My question is when the Weasley parents were Hogwarts students. They appear to be younger than Voldemort, and Molly mentions Slughorn rejected Arthur for the Slug Club. Also, Bill is about 25 in the series, so he was born about 1970.
In GOF, Molly says that the gamekeeper Og caught her and Arthur out after dark, and gave them a beating. However, in COS Hagrid was gamekeeper since the 1940s.
According to their Harry Potter Wiki pages, Molly was born on 30th October of either 1949 or 1950 and Arthur was born on 6th February of 1950.
Therefore, Molly was either in the same year as Arthur and they both went to Hogwarts from 1961 to 1967 or she was a year senior to him, with her graduating in 1966 and him in 1967.
Going by the Pottermore fact file of Arthur, he was born on 6th February of 1950 and hence he would have attended Hogwarts from 1961 to 1968.
Molly Weasley is more of a grey area. Here's the speculation from the Harry Potter wiki (emphasis mine):
Bill Weasley is the oldest Weasley child and was born 29 November 1970 (Pottermore - Bill Weasley). Molly says that the Whomping Willow (planted 1971) was after her time at Hogwarts (GOF, Ch. 31) and that Molly and Arthur eloped soon after graduation (HBP - Ch. 5). In order for Bill to be conceived in wedlock, Molly must have graduated by June 1969. Given her October birthday, this graduation date requires she started Hogwarts in 1962 and was born 1950. However, as Arthur Weasley was born 6 February 1950 ( Pottermore) he would have graduated June 1968, so if he and Molly were in the same year, she would have been born in 1949.
So, assuming she wasn't pregnant before leaving school, she either attended Hogwarts either from 1961 to 1968 or from 1962 to 1969.
