In my experience, even if you stay frugal, and I did, the main change comes from the job requiring full-time hours (and some weird culture stuff). I worked part-time in college and programming hasn't changed, but then I had daylight hours to walk outside, the freedom to stay home if I felt sick, etc. I started working F/T and almost immediately, the hour+ commute and not seeing daylight in winter rewired my brain. Suddenly, my mornings were spent preparing my lunch so I could go to work, my evenings cooking dinner and recovering from work, and on the weekends, I did everything except talk about work. (In those days my partner was still a student, and it made the contrast greater).

After the first year, my work had become my only source of pride; after the second, I was constantly wondering how to be better at work; three years after that, I engaged in a hobby for the first time in my adult life. It snuck up. I don't like money that much and I never made the conscious decision to prioritize my career; but it ate my life and I doubled down because it was all I had left.

The fact is, for most young adults, jobs pop into their life right on cue to replace the family they're no longer seeing and the dreams that have disappointed them (around 25 where that first crisis hits). If you're 25 and lonely do not go to work happy hours. If you're bored don't take work home. When your boss tells you you're very promising and he can see you grow in this company, tell yourself you're an interesting person who's had a life full of stories that people would love to get to know. The best promises are the ones you make yourself.