Fathers of daughters, at what age would you allow your daughter to spend the night at an S/O's place?

I'm 22, my girlfriend of 6 months is 21 and soon to be 22 this summer.
This is the current situation:
To save money, she lives with her mother, step father and younger step sister. All of which are great people who like me and I like them as well. Her step father will not allow her to spend the night at my apartment under any circumstance. She can however, stay as late as she wants under the condition that she returns home at some point to sleep. Step father is operating under the rule of "my house, my rules". This has resulted in me typically driving her home late at night (10pm-2am the latter being rare but it happens sometimes)
Admittedly this has been a bit frustrating. Not only is it inconvenient because it's a 40 minute round trip to her house and back but I'm starting to get worried about the possible dangers associated with driving that late. Don't get me wrong, I sympathize with the step father. Even the thought of having a daughter scares me sometimes because because boys/young men can be **** heads and he knows what were up to when she's over here but man, is it worth it at this point? What if we got hit by a drunk/tired/distracted driver while I was driving her home late at night? Would the pride of authority over your step daughter still be worth it if you got a call from the hospital?
I don't know what to do, I've talked with her about it several times and every time she explains how there's no winning with it and her step father will never budge as long as she is under his roof. If you were her step father, what would change your opinion on something like this? I guess I'm just trying to get in the mindset of her step father so we might be able to make some kind of progress or compromise because the current system just isn't working. Any input is appreciated!
Edit: Context about us- we're both engineering students, in good standing with her parents, and have been generally as responsible as any typical college student can be. Never been into drugs, arrested, fired from a job, both over 3.0 GPAs etc.


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Source.

Hmmm