It is already the law where legal consent is restricted by authority until 18, so if one party has legally recognised authority, responsibility or in a position of trust over the other, then the other person cannot consent so there is already a step towards recognising 16 and 17 year olds are vulnerable (though people tend to forget that 16 and 17 year olds can be in that position of authority).
I'm not against the idea of adding in legal consent restricted by age difference for teenagers, there are plenty of places with those laws alongside legal consent with restriction by authority as we have and unrestricted legal consent though I'm not certain where to draw the line on it or convinced how much it would solve this type of issue beyond what current laws do.
You’ve got to draw the line somewhere though. 18 at least means you have two more years of being an “adult”. You’re not in school anymore, might have had a bit of experience of working, met a much bigger cross section of people, are more likely to have had at least one relationship. You couldn’t really make the age any older than 18
Except the school leaving age has been raised to 18 in England, and even before and beyond that, there are plenty of 18 year olds in schools. There have been issues raised around how safeguarding guidelines including KCSIE on paper leave out 18 year old students. More schools are catching up and ensuring it's in their safeguarding guidelines, and personally, I'd like those KCSIE to be changed to recognise and ensure protection of all pupils, including 18 year old Year 13s, are equally protected.
And if we're going on laws in other countries as examples for changing ours, there are examples where the unrestricted legal consent is above 18, largely brought in because of issues in schools and sports where predatory types were targeting 18 year olds still in school or junior sports. I've seen unrestricted legal consent as high as 21, working alongside legal consent restricted by age differences for those younger and legal consent restricted by authority. They're usually brought in when something really bad has happened that enough people want to prevent happening again.
You either believe you can consent, or not. You can’t really say you can consent at 16 to sex with another 16 year old, but not a 19 year old. And what would the line be? What is “okay”? 16 & 18 okay, 16 & 19 not okay?
The law already does that - a 16 or 17 year old cannot legally consent to a 19 year old - or even another 16 or 17 year old - who has legally recognised authority over them. This does happen - there are 16 and 17 year olds who are apprentice TAs who work at secondary schools and sixth forms and so have legally recognised authority over those pupils.
In England, we already have varying types of consent. We have literal consent at 13, legal consent restricted by authority at 16, and unrestricted legal consent at 18 currently in place in law, as well as varying laws that that have been previously which can still be invoked if the crime happened at a time those laws were in force. When we have long-term perpetrators, we can end up dealing with 2-3 sets of charges to cover the time span.
Any new changes that bring in legal consent by age differences would be added onto that, as they have in many places. What is legally determined is okay I think would take a long debate - and likely something seriously wrong happening that gets a lot of visible attention that makes brings public pressure to react, much like our current laws around legal consent restricted by authority. Or if public opinion really swung in that direction - I think there is some cultural push in this direction.