My daughter wasn't allowed to date until she was 16. Fortunately, it really wasn't an issue, because she horseshowed extensively which meant being out of town a lot (either at a show or at the trainer). Most of her friends were in the horse show world.
Because we've spent so much time together (traveling in the truck, washing and tending to horses, staying in hotel rooms, etc.), we have a very open relationship and talk a lot about everything (including whatever boy she liked or was seeing at the time). I would say that she involves me in most of what goes on in her life. I am NOT her best friend (that's not my job), but I am her confidante in most ways.
As someone else said, the topics of the conversations depended on what was happening at the time. We talked about the goals that she has set for her life and how choices that you make as a teenager can impact those goals. Sometimes I had to sit back and let her learn some things for herself (one friend comes to mind that she had to learn on her own wasn't the friend that she thought she was - more of a user).
I didn't say, "Don't go parking!", but I did talk about how situations can get out of hand (even though those emotions were completely normal) and that sometimes we have to live with the consequences of actions that we wished we could change and how others can be hurt. Had the same discussion about alcohol and drugs (peer pressure seldom leads to the best choices for an individual). I didn't just bring these things up once, they came up numerous times as other kids she knew ran into some problems (talked about how they might could have avoided their situation).
If she decided the time had come to end a relationship, we talked about how she was going to do it (you don't just dump somebody and pretend like they never mattered - you owe them more than that). You play fair and treat them like you would want to be treated (you don't sneak around). Sometimes she was the one who was "hurt", and we talked about taking the high road and that you don't chase after guys. High drama was discouraged strongly

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She's 19, and the guy she's dating now is 23. They've been together for 2 1/2 years (except for a 6 month break up). We've never had a problem with the age difference because of the boy that he is (and the girl that she is). Their dates have always mostly consisted of going to get something to eat and then coming back to our house to watch a movie (generally back by 7:30 or 8:00). They're both involved in horses, so that's also a part.
Have I "picked" her dates? No. But I have on occasion told her when I thought somebody was unsuitable for her and why, and thus far, she's always taken that into account (probably because she knows we try to be fair and open minded).