I think it's incredibly important for young men and women to learn what it's like to live on their own before serving a mission. For most people, I don't think it's a good idea to turn in papers and leave fresh from high school, even if you are old enough. I think it's a much better idea to have at least one semester of college away from home first, because it will help prepare you for the responsibility that a mission entails.
(link.)I think the age change was a great idea. My brother would not have done well if he'd gone to school before his mission, but I have all confidence in him that he will succeed when he returns. For women, it helped remove the stigma of going on a mission just because you weren't dating anyone or couldn't get married. Although there is a lot of added pressure to go on missions earlier for both men and women, I think that's starting to dissipate, especially with the counsel given by Church leaders.
In my stake/seminary class, I'm surrounded by peers who choose to go as soon as possible, sometimes graduating a semester early just because they can. One young man emphasizes that even though he's won't be 18 until September, he is anxious to serve as soon as he is allowed.
Back in February/March, I went to a local fireside with an LDS inspirational speaker. At one point, he expressed his concern about statistics he'd heard suggesting that only a fraction of "eligible" young men are going out on missions. I didn't know what to think about his comments. Yes, there will be a period of time where I'll be "old enough," but not already out. It might be a year or longer. But... I'm trying to accept that, and to be okay with my reasons. That speaker seemed to think that if an eligible guy wasn't going, it was because he had some sort of "problem."
I've recently told quite a few people that I won't go on my mission right after I graduate from high school this spring, but that I will be at BYU in the fall. The responses I get are hesitant, generally something to the effect of "Oh... I guess that plan could work too, if you really think it makes sense for you." (In other words, people are uncomfortable with the idea that I would actively choose to delay my mission.)
There's plenty of cases where I think it makes perfect sense to wait a little bit. Still, I'm confronted by the attitude that I must have some "worthiness issue," or that my testimony must be lacking, or that I must simply not be working hard enough. I'm fairly certain those aren't my reasons. (Maybe, to avoid these conversations, I shouldn't volunteer my plans to the people around me until they ask. But oh wait, that's what I already do. And they still ask rather probing questions. While I struggle to explain myself.)
If you're a young man, you either need time to adjust to responsibility at school before the mission, or you need time to adjust to hard work on the mission before you have to deal with school?