This is all mostly true, and since I hate debates about the bible, the only thing I would like to point out is that even if theoretically a 15 or 16 year old girl could be smarter (or as smart) and "more mature" than a 19 year old one doesnt change the fact that the human body and brain doesnt really finish developing until around 20-21. So theoretically again, said 16 year old could possibly be a completely different person by the time they are at a suitable age for marriage. At 19, there is little chance for a person to change as drastically as they possibly could just a few years earlier.
I agree with what you said for the most part. However, a person, in general may not be finished changing mentally for years to come. A mental maturity is far different from a physical maturity. In the USA, there are states that slap the age of 16 on legally able to Marry. There is...unless it changed,(it may have) a state that allows you to marry at 14. In some countries...dating a younger person is allowed...but there are rules to the encounters. Physically a person could stop changing as young as 15, (in my case =/) or they may get a late growth spurt. Mentally...well that's another story.
Now that I've said that:
A person can change drastically from the age of 19 to 21, persay...mentally. Their mentality, their preference in the opposite sex can change in ways you'd never believe. I've personally seen cases where women and men have totally different interests in the opposite sex than they had just 2 years prior. However, there is the case where some people truly have matured mentally at an earlier age. In some cases...people at 14 may be the same person when they hit 20 or 21. It's truly a matter of case by case. Now, in the case of the US...there is a limit before it's truly frowned upon. I believe it's 3 years. I don't truly see a problem with an 18 year old dating a 15 year old or a 20 year old dating a 17 year old. That is, so long as they are within the boundaries of the law. Also...it might be a good idea if the parents of this child in particular are approving of it. If there is no problem...then so be it.
Personally:
I haven't changed much in my mentality as far as my choice in women from when I was 10....I'm 24 now. I still know what I like in a woman, and it hasn't changed, essentially. I know now, that I prefer women who are older as opposed to women who are younger or my age. I've always liked women who were older, but I had no real preferrence when I was younger. Due to my experiences...I feel now, that older women are more my style. However, I don't just automatically shut younger women, or those near my age range out.
A gap:
Well once you become an adult...the gap between you and another adult is all up to preference and also agreement with whom you wish to pursue a relationship with. My own parents are almost 8 years apart. However, contrary to popular situations, my mother is older than my father. They started dating when my father was 19. The age gap between my father and my oldest brother is almost the same as me and my oldest brother. Again, that's between the two people who are making the decision. It is true...the older you get the bigger the age gap.
Referring to Suspect's question:
Talk to the person...there's nothign wrong with a conversation. There's nothign wrong with keeping a friend, and providing that older figure in their lives. Wait until this person is an adult, and if they happen to be interested in you...then it's up to the two of you to pursue a relationship. I'd give....say an age gap like myself 24 and say...a 17 or 16 year old girl. That's a 7-8 year difference betwen myself and the person...pretty darn big gap. It'd be rude to just cut the conversation short...but make sure it stays casual. If you need to find a way around it...just be the "busy" adult with many things to do. Keep the relationship as casual as possible play the older friend who listens. There is truly no need to cut all communications off. I feel a friend is a friend...age gap makes no difference.
Referring to the Bible reference:
In essence, you are correct, and the bible is crammed full of amazing advice that, in principle can be applied to our modern times. As long as the law allows, certain things happened. Polygamy for example, was allowed up until a point when it was put to a stop by god himself. So yes.....a rather large gap COULD be allowed...so long as it's within the law. That is going by bible standards, of course. I don't believe this is, nor should it go into a debate on the bible.