I definitely think there was a shift towards the end of the 90s.
We were heavily influenced by American TV/Movie culture...Dawson's Creek, Buffy The Vampire Slayer, She's All That, 10 Things I Hate About You, Cruel Intentions, Mean Girls, Never Been Kissed, Bring It On...all of which featured Prom, Homecoming Dance etc.
This was the era of Britney Spears, Christina Aguilera, N-Sync, Backstreet Boys etc and US and UK culture were becoming far more aligned. It was the in thing to be wearing US labels, Abercrombie & Fitch, Hollister, Calvin Klein, Tommy Hilfiger, DKNY. UK bands like SClub7, Steps, Spice Girls etc quickly collaborated State Side and were filming their videos out there,
wearing US clothes etc. I think there was a case of us seeing what was marketed at us and wanting a piece of it for ourselves. US High School culture looked more exciting than our own...and we started to want a bit of it for ourselves. At my school, we campaigned for a Cheerleading Team!
My next youngest cousins are 3 years older...they didn't have quite the same experience as us but within a few years,
something changed. The way all of a sudden we all had mobiles and the internet but hadn't just a few years earlier.
My Mum and her friends never had fake tan, nails etc...but when St Tropez spray tans came about and acrylic nails became popular it seemed to take off fast and become a big part of many women's going out routines. Again, this really took off in the late 90s.
My SIL (Irish funnily enough) was the first person I noticed getting all of this done in about 1999. At some point spray tan, fake nails etc took off and became far more popular that they'd ever been. Same with hair straighteners. So I think some of this was a change in beauty technology and trends, that happened very quickly.
In the 80s and early 90s you rarely saw fake tan on anyone. Look at how fake lashes, brows, curly blowdrys, lip filler etc have all taken off in the past 10 years...some of the grooming pressure simply stems from changes in beauty routines. In the early 90s it was all bushy eyebrows, perms and heather shimmer lipstick - fashion changed fast.
The boys were also getting stuff done that they hadn't previously...fake tan, highlights, straightened "curtains", shaved eyebrow patches, piercings etc. I don't know if it was just the age I was but I feel like we were all suddenly very image conscious, in a more intense way than before.
Limos to the balls had long been a thing though, locally.