Voldermort is Gone Tom Riddle Is Here
Voldermort rose in Draco Malfoy's 3rd. At the end of the year. They did not know why or how or what happened. They had been attempting it, Draco knew despite his father's tight lips. Yet, the process had not gone as planned. It was the soul from the diary that had returned, not the 20-odd year old that they had been expecting. This came with...complications.
Tom Riddle was 16. Ideally, he would go to hogwarts in order to recruit those that would remain loyal to only him. Sure he had the remnants that his older self had recruited, but Tom did not know them, and furthermore, he doubted the viability of many of them. So he uses them, but he wants more loyal followers, and as such he needs to go to Hogwarts. Quite a decent foundation for such things.
Using the young Draco Malfoy, molding him, grooming him, he would fool Albus Dumbledore, gain access to Hogwarts, and then he would begin his recruitment process. If he found his mate, became a bit too attached (obsessed) , and started another feud, well all part of the process he supposed. There were other issues as well. With Remus Lupin, the werewolf, still teaching, and the favoritism amongst the students, they had some work to do, but it was nothing Tom couldn't handle.
