Quick Danganronpa question (SPOILER?)

If you know Byakuya togami was in danganronpa 1 but came back to v2 to investigate if all of the ppl in v2 are 3rd years 17-18 and byakuya came back twice (so v1 he was 18-17) wouldn't be be 20-21? since another 3yrs would pass by.