I think you're right on track. I'm 41, 18:20 5k and 1:24:52 1/2. You're younger and faster. The only question is how many 1/2's have you raced? I don't think you'll need a ton of "experience", but it does help a bit. It's my favorite race distance, more so than the full because you can push it more, still suffer, but just for a bit less time and recover faster. Nothing wrong with a positive split either. I'd rather cross the line on the edge of "nothing more to give" than feel like I could have started a little more aggressively. Going out around 6:20 should be fine, you'll know within a few miles if you can pick it up and really go for it. Ideally you'll have some other runners with similar pace to run with, that is such a huge help vs going it alone. Best of luck, a fast 1/2 is the best way to qualify for NY Marathon if that ever interests you too, skip the lottery!