Enlisting/Officer Air National Guard?

The question

I am 27 and a junior finishing a com web design degree. I am debating joining the Air National Guard. I am all setup for MEPS next week, but I am starting to reckon instead of going in as an E3 I should wait till I graduate. Any input on this? I’ll graduate Spring 2013. I have a high GPA etc. I just worry 27 is a bit ancient to enlist, and I may do better waiting and trying to become an officer. Going enlisted I’m looking at a $ 20k sign on bonus. I assume it will be taxed to $ 13k which isn’t all that much. When I was 19 would have been a different tale. Loan repayment doesn’t exist for ANG anymore.