This would be so easy if they weren't in the power dynamic of being the boss's daughter and employee in addition to the age gap. I don't think it's ever stated how old Takamura is, but Senko is somewhere between 15-18 since she's in high school. I think she's probably closer to 17 or possibly even 18, but it's still an age gap. I mean, I guess Takamura could be in his EARLY 20s, but he's old enough to drink and so is Ruka (right?) which means he's older than her and probably at least 21. I dunno, it's manga so it doesn't really matter, but it's still something to think about.