On the "Dear Bro Jo" discussion page on Facebook, a girl asked a question about dating guys who didn't serve a mission. This was my very opinionated response.
I see a "red flag" as "Stop and back-up." I'm not sure that's the correct way to look at someone who didn't serve a mission. I see it more as a "use caution," which is why I said it's a "yellow flag."
First off, I don't think it's something that should need to be brought up early on. I know a lot of women who ask guys if they served a mission right in the first conversation. I don't agree with that at all. Asking someone if they served a mission while you're just getting to know him is possibly asking them for information you don't need to know just yet, because let's face it, if he says no, you'll wanna know why.
Now, if it is a point where the subject is appropriate to discuss, and he says no, you have the right to know why. This is something that I think should be talked about around the stage 5/6 in the levels of a relationship. At that point in time, you know each other well enough to be asking that kind of information, you know enough about each other already to be able to honestly look at him for who he is now, and you're not too emotionally involved.
Already knowing the person is important though. Sometimes, people may have a very complex reason for not going. It's a legit possibility.
Now, some reasons are red flags. One of them being he wasn't worthy. Being unworthy all the way from 18 to turning 26 in the MTC is a LONG period of unworthiness. At this point, you should really be careful. Now, if he has truly repented, is truly a changed man, is a worthy priesthood holder, and has/is working towards a Temple Recommend, than I don't think you should hold it against him; however, if he isn't worthy or honestly working to change, than leave him be and move on, especially if his unworthiness involved pornography. Honey, if he isn't winning his battle, don't get involved. It WILL hurt you.
Another red flag is if he is nonchalant about not serving a mission. If he doesn't really wish he had served, than he isn't converted to the gospel. He may very well have a testimony, but there are a lot of inactive members with testimonies. A testimony doesn't guarantee a person has converted to the gospel, and only someone who is converted to the gospel is worthy of a righteous Daughter of God.
There are thousands of possibilities and things that could be listed, but the important thing to remember, is that being an RM doesn't mean he's a great guy, is converted, or is worthy. An old bishop at the singles ward i used to attend said the percentage of RM's who hold current Temple Recommends is "a lot less than y'all would think." Not being an RM doesn't automatically make someone less qualified to marry. Who he is now is a lot more important than who he was 5, 10, or 15 years ago.