ny runner, I'm in almost exactly the same situation as you are. I also have not been running much for a few years and am also aiming to run a 1:30 spring half marathon.
I think that you should definitely aim for the spring- 6 months is plenty of time as long as you start trainig consistantly. I'm doing a half this weekend after only training for a month because I hope that it'll give me a better sense of where I'm at and will make the distance seem shorter in the future. I plan to run 1:45 (8 minute miles), but am a little concerned about the last few miles.
After this weekend, I plan to start putting some 7 minute miles into my regular runs, and gradually increasing that until I'm running 7 min pace every other day and for my long run. I've run a 1:34 half off just that kind of training. This time when the race gets closer though, I'm also going to do other kinds of workouts.
I'm excited to hear about how your training goes!