We didn’t make the rule, so we don’t know for sure—but here are a couple of ideas.
Idea number one: You mature a lot between the ages of fifteen and sixteen. Generally speaking, a sixteen year old is better equipped than a fifteen year old to handle the temptation and pressure that accompany dating.
Idea number two: Studies have shown that teenagers who begin dating early are much more likely to be immoral than the teens who wait to date. For example the same study quoted above showed that 70% of teenagers who waited to date until they were 16 avoided immoral activity, while 80% of those who reported dating before they were 16 had become sexually involved enough to need the counsel of their Bishop (see Bruce Monson, New Era , 6/01, 36).
President Hinckley offered his wisdom on the matter by saying,
The Lord has made us attractive one to another for a great purpose. But this very attraction becomes as a powder keg unless it is kept under control. It is beautiful when handled in the right way. It is deadly if it gets out of hand. It is for this reason that the Church counsels against early dating . This rule is not designed to hurt you in any way. It is designed to help you, and it will do so if you will observe it ( Ensign , January 2001, 8, emphasis added).
If you can wait till you are 16 to date, then you can wait till marraige for all the rest. Not only is it “just the age” but its also something that if we can be strong enough to follow, we can be strong enough to do all the rest.. I know it may be hard. Especially when that cute girl digs you or that great guy asks you out.. But it actuality, you are better off at such a young age to stick with many friendships rather than one boyfriend. By doing so, you often loose sight of more important things in life and become distracted by young hormones etc. By waiting till 16 you can prevent that. And hey, you get a few blessings too!