You said "many 19 year old women have more sense and maturity than a man in his 30s".
I work with teen girls. Yes, they're more mature than their male counterparts, but no, on no planet are they more mature than the 30+ year old men I know. Mentally and emotionally they're still very much children – even those "mature", "reliable" ones – in so many ways I could go on about.
Also, for that reason, I would not advise most teen girls to romantically or sexually be with 30+ year old men (this is not about Diana at all, but about the fact that I don't believe your claim about your comparative maturity).