As far as the stages go, let’s assume they are doing what they both are expected at the current age.
The 35 year old male probably has an established career, can legally drink, probably has friends in that age group. May own a home and is living alone, maybe room mates
The 18 year old female just graduated high school, getting ready for college. May or may not even know what career path she wants. She can’t legally drink yet in public. Still lives with her parents, probably unlikely to be financially independent at this point.
Just doing 2 completely different things. Now you’re correct that we afford 18 year olds a certain level of legal freedom and if she wants to run off and be with a 35 year old man she’s certainly fine to do so even if it’s probably ill advised
As far as the sex aspect goes, once again, completely legal for them to engage in it as long as he’s not manipulating her, no problem
I’m curious if there is any age gap with an 18 year old you’d find odd? 18 and 40? 18 and 60?