In previous decades, there were pop songs brazenly celebrating this.
My Sharona is still regularly played on the radio.
Rod Stewart's Tonight's The Night.
You're Sixteen, You're Beautiful And You're Mine (if the male singer had also been 16 or 17, why would it have been remarkable in the first place that the girl was as well?)
Young Girl by Gary Puckett.
Diana by Paul Anka is the other way around but still somewhat iffy.
It was clear what single theme the Undertones song Teenage Kicks was about. There's no particular suggestion from the lyrics that it wasn't about similarly-aged young adult lovers (Feargal Sharkey was about 19 when it was released). However, John Peel, who was nearly 40 when the song first hit the charts, unswervingly hailed it throughout his life as his favourite song of all time. I'm amazed that he went largely under the radar for so long and, indeed, still has never really been condemned for it. He was a known predator and apparently got a 15yo pregnant.
The word 'teenager' is frequently used as an ambiguous catch-all in this context. I really don't understand why it's universally considered such a useful word anyway when generally discussing that age range as 13 and 19 are obviously such different stages of life and maturity.
I also notice an alarming number of people (male and female) who will casually insist on referring to grown women of all ages as 'girls', which is annoying enough; however, that has led to a disturbing trend for people to thus go a step further to differentiate and specifically indicate that they're referring to women in their very late teens and twenties by describing them as 'young girls'. As well as being monumentally patronising, this only serves to blur the lines and can provide the careless talkers of this proclivity with a widespread cloak of deniability, allowing them to backtrack and rely on social ambiguity.