How old it too old for a spanking?

I got woken up last night by the sounds of spanking coming from my sisters room. It was around 10:30 so i;m guessing my sister (13) was definitely out pass curfew. I didn't ask any questions this morning, that would have been awkward lol. I'm not sure if my mom or dad spanked her, but it sounded like hand on bare skin. Does it make a difference which parent spanked her? Is 13 too old for a bare bottom spanking, and is 13 too old for a spanking in general?
How old it too old for a spanking?
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