Good luck! I'm also a career changer (33, former Pharmacist Recruiter, Fortune 100 company) and just finished my last CFI rating (MEI, CFI-single, CFI-I through ATP self-paced program) and will be interviewing at a couple flight schools next week. Keep your eye on the prize, put the same effort into school as you did work (which will be easy), and you'll be fine. The road seemd very long at times but I constantly remembered the day I decided to make the switch. All career changers probably remember that particular day - when you just couldn't bring yourself to turn on the computer in the morning knowing what was waiting in the inbox, or dreaded coming in and seeing the voicemail light on the phone on knowing there were 20 messages with BS problems that needed to be solved RIGHT NOW and that light had been on since 5 minutes after you left at 9pm the night before. From the outside it seems like a dream job - inside a nice climate controlled building, not physical labor, well paying. But to some (me and probably other career changers as well) those things weren't worth what the job took from us - BS meetings, soul sucking Corporate Culture, and the fact that on a 1 hr daily commute you knew over half the license plates around you at any given time because you were all in the same pack of sheep.
Do not worry - you made the right decision! Give it hell!