May be people who you have met, and I agree that constant inner monologue can be grating to the player (although there are way worse examples out there). But yeah, dwelling on consequences and a possible development is something that happens in heterosexual males, too. It's not always and exclusively "woohoo, I scored!". And having had a girlfriend with around this age difference, some other questions come into it, too, like long term prospects - you might be willing to settle down, she is in her early 20s and might not.
Also I'd argue that especially Abby's attitude towards MC would be significantly different if he were a less dwelling type.
As for "you've done the deed so get on with it" (I thought I had a post quoted for that but apparently I haven't): real life isn't a VN, you unlock a scene and you can rewatch it again. You or the other side might have second thoughts, circumstances might have been strange, having taken a step might make you or the girl realize the way you're going even more. Granted, with consenting adults of approximately the same age and no complicated circumstances (one is in a on-off relationship, workplace stuff, change of dynamics in a close circle of friends) things will probably continue like that (or end one day) but the moment potential problems may arise, sometimes people will take a step back. Also, just stuff not being illegal does not mean that it won't have consequences on your social standing and suchlike - depending on your surroundings, "off the norm" relationships can easily lead to you being shunned.