Whilst I'm here, any recommendations for fun nightspots where a 21 year old and a 48 year old will be equally comfortable would be happily received

Can casino-hop (and earn next year's offers) playing tables. The drinking game of choice (= as long as you are still sober enough to see your cards) was always Pai Gow. Now there's a lot of face-up Pai Gow available where the dealer sets their hand first, managed some sessions there with my daughter, very hard (but not impossible

) to lose much, table service drinks pretty quick and then hop to next place.
Beer Bark (Paris) and Brewdog both with decent rooftop bars, various bar games on offer, not sure about that in Dec tho.
Some reasonable tribute acts playing lounges with cheap tickets, duelling piano bars (eg NYNY) quite good for an easy night out. Casino lounge bars such as Heart in PH can be quite lively. Usual show tickets, some free or discount on MyVegas. After that, I guess its full on nightspots, not really my thing.
Have a great time, enjoy your daughter's 21st, she looks beautiful.