As others have said, absolutely no problem with a 16 year old watching Sex Education.
I would also like to thank @HiveQueen for the www.commonsensemedia.org recommendation.
I used it to have a look at what it says about Buffy (Buffy the Vampire Slayer aired on BBC2 between 1998 and 2003) which I remember watching every single episode of at the time.
This show is currently on Amazon Prime and is well worth watching. The overall rating on common sense media is 12+ but a number of reviews do mention that the earlier seasons are more acceptable for younger viewers (perhaps 8+) and that later seasons are a bit more adult - maybe 14+.
I found this sort of nuance really useful and it coincides with my thoughts as well. So that makes me a lot happier to use this site in future when I come across shows that I haven't seen before.
What is very odd though is that Amazon label every single episode of Buffy as 15+ and always include warnings "Drug use, foul language, sexuality, violence."
To be frank, rewatching Buffy currently, I have never seen any drug use or foul language at all (perhaps though they were referring to a person described as being a witch who was going to cast a spell?).
With sexuality, I've currently rewatched 59 episodes (currently on season 3 - yes, I'm binging over Christmas) and I think there have been two times where there has been sex referenced. Buffy loses her virginity in season 2 (which isn't shown) and then she has a flashback where all you can see is rustling sheets and Buffy’s face with her eyes closed. It’s very PG. And then two characters briefly have sex in one episode in season 3 - again very PG.
Apart from that, the only sexuality I can think of in most episodes is people kissing or holding hands.
Then, when it comes to violence, yes there is violence but rewatching it now it does, for the most part, seem more funny than threatening compared to many other TV shows currently available.
For anyone old enough to remember the old Batman TV show with Adam West that used to have repeats on when I was young, then the level of violence is, generally speaking, no more than that.
However, it must be said, that it does show vampires regularly being killed. This is done by thrusting a wooden stake into them and they then disappear in a cloud of grey smoke.
Overall, the sexuality and violence is way less than in anything like Twilight which, I believe, also had a 12 certificate.
So it does seem like Amazon are a bit
but that common sense media site does seem to be really useful.