How old Am I?

So here I am 25 years old, acting like a high school girl. Granted in HS I didn't have sleep overs with the opposite sex, but some how I'm around a guy now that has turned me into this little high school girl. I've never had a problem being forward with a guy, or letting them know what I want....but for some reason, when I'm with this guy, I'm this shy girl that can't let him know how much she really likes him. So the question is now what do I do, or how do I get out of this shyness?