In the first part he was a senior in high school but by the second part they'd been together for about 2 years or so, he was in his second year of college.
The mangaka once posted in her twitter their ages and birthdays, and there it tells that Hazuki is 20 years old(21 if it is irl as his birthday is on August 7). He also works as he has a part time job in his mom's hotel. It is said to be a preparation for him as he will inherit her business.
Thanks so much it makes so much more sense now.
So I know the seme got older as the story went on, but how the old is he? At first he said he was 17 so I thought he was in highschool but then they said he was in college then university? After that too there was not a clear sign of a time skip beaides the new baby but he was working now? Still love the story though