I think it's quite bad that people are being so judgmental towards the person that asked the question; even if you don't believe in what he is proposing, it does not give you the right to be so rude (frankly); he is only looking for honest advice as to what to do, and thought this would be a secure and open environment to do so. Please bear this in mind before answering.
Now, back to the question, I'm going to be a typical A2 English student and analyse this methodically. Please bear in mind that these are just my thoughts - I haven't been in a situation like this so I'm basing it off what I would deem as appropriate arguments.
PROS:
1) From the way you described it, it seems that you are both committed to the idea of being together
2) You are clearly good friends with her, which a good building block for romantic relationships IMO
3) You have been open about it with her parents, so you don't have to go behind your relations' backs, and she will feel comfortable with your circumstance
4) You seem to have taken a mature attitude towards the idea of the relationship by waiting for her to be 16, and have been patient
5) Being in a relationship with someone more mature may help her feel safe with first experiences e.g. sex, because your post suggests that you are also very mature and would not abuse her innocence
CONS:
1) Although it may not seem so in a few years time, the age gap will seem HUGE at the minute. This is because in childhood development, because adolescents are still in a learning stage, each year means huge progressions in maturity levels. Even if she is mature for her age, this does not prevent this maturity issue from being a huge hindrance
2) Given her circumstance, this may not be the right time for her to enter a serious relationship, especially due to (1). She is about to do her public exams, inevitably one of the most stressful periods in her life, and she honestly doesn't need relationship stress to add to that. Balancing revision and hobbies may make it very difficult for her to give you attention, and the last thing you want is to be a distraction, because these are some of the most important years in her life, especially if she wants to pursue higher education
3) The fact that you originally stated you were 22 and she was 16, but then conflicted this by saying you are actually 23 and she won't be 16 till next year sends across mixed messages about your patience - you don't want to rush her into doing things she doesn't feel comfortable in doing; just because she is turning 16 it doesn't mean she will want a full blown relationship straight away now she's legal
So while there may be seemingly more pros than cons, the severity of the cons mean that we should take them into greater consideration than the pros. Personally I would say to avoid entering a romantic relationship now, because I wouldn't say this is the right time for her due to her position in education and because of the vast difference in maturity. If I were her, I certainly would turn you down if you asked me in the same way you intend on asking her, not because I wouldn't care for you, but for the aforementioned reasons. However, this isn't to say you should break off contact with her. It's fine to stay in an amicable relationship with her, but I would just advise you to wait for a bit for her to fully mature and to get this period of her life over with. If you truly love her, you owe it to her to let her go for a bit so she can achieve what she wants career-wise. I would say maybe when she's at least 18 would it be OK to start considering it again.
That's just my opinion, and I wish you luck with your situation.