As a early-30's programmer who is back for a MS in EE/CS, I've made a number of friends with grad students in fields that are quite science and computationally related. I'd recommend looking into:
Linguistics, especially Computational Linguistics
Cognitive Science, especially related to AI
Computer Simulation ... especially Agent-Based Simulation, which can be applied, IMHO, to a lot of sciences.
I'd also second the previous posts on Bioinformatics and Computational Physics.
Also, I always strongly recommend that if you can get a PhD, you should. In the US, the statistics are quite stark, only 30% of PhDs in Science, Technology, Engineering and Math are awarded to US Citizens. What's going to happen when all those Indian and Chinese PhDs start going home?
Best of luck!