Level 20 is sort of the "soft max". beyond that it's very expensive to progress further. It's 210,000 total XP for level 20. 435,000 total for level 23.
Realistically, say 4 hours of catching at those lured sites buys you enough for the 60 evolutions, 60,000 xp. Let's go with 5 hours total.
Perfect conditions, i think that comes out to 35 hours. I'd say double or perhaps triple that realistically. You have to go gather loot and stuff, which still grants XP, just at a slower rate. If the OP felt like it, running the whole time with lucky eggs would cut that down quite a bit, maybe half, and cost perhaps $20. I'm guessing around 80 hours without buying anything.
A single person who's interested in it can pretty easily come up with 3 hours a day, and quite a few hours on the weekend. 30 hours seems pretty accessible. it's been out for 2 weeks or so now, so the OP is only a little on the high side. Perhaps not at all if they'd spent money on eggs.
Of course, different people have different commitments. In a rural area, this would be impossible. Family, hobbies, a long commute would drastically reduce the time available. But if your hobby is video games, it's pretty easy to swap one for another with little effort.