To Sign Up For Preschool, or Not Sign Up: What A Difficult Question!

Preschool seems like one of those things that all kids do, it's part of their education, right? My initial answer to this question for Bug, was kinda on the line of "duh!" However I then remembered that I, myself, never went to preschool.

Bug turned three years old this winter, and with his age, grew a burning desire for him to start school. Until then he was extremely fascinated with buses, and felt compelled to ask every other kid he saw if he could go to school with them, but he didn't outright start asking to go to school until a few months ago. I assumed it would pass and he would enjoy his time at home again after the bus was out of site, but this wasn't the case. He would throw fits, crying and sobbing because he needed to go to school! So J and I sat down and seriously discussed Bug starting school this Fall. The biggest question we immediately asked each other was, "do you really think he's ready?"

Bug just turned three, which means when school starts in September, he'll still be three. Isn't that a little young to start preschool? Apparently, it is not. Preschool in our area is available for children ages three to five. This is amazing, except for the price of sending our son to preschool. I thought a public education was supposed to be free? I guess that doesn't apply to "preschool" where your children are supposed to prepare for "real" school. So now that we know we have to pay to send him to preschool, where do we go from here? How do we know he's ready and will get a good use of the preschool program?

• Can he count? Yes, he can count to 15 if he feels like it! Which isn't very often.
• Can he sing the alphabet? No. He realized that it's to the tune of "Twinkle Twinkle Little Star" and that's were his mind immediately goes. 
• Does he get along with other children? If "getting along with" is code for "stealing toys from" then yes. Although, if he makes another kid cry, he's good at giving hugs. However, if you've ever watched the news, you are probably thinking the same thing as me, in that he'll hug the wrong person and his parents will sue my three year old for sexually harassing their three year old. So I have to teach him not to hug people.
• Does he listen, or follow instruction? *uhm* Maybe this won't really be a requirement yet?

So, I'm stuck. On one hand, I feel like I'm crushing his dreams by not sending him to school soon, but also feel he needs more time to really understand why he's going. On the other hand, I really think that there has to be other kids at his level, and preschool is something that would really benefit him and get him up to speed for Kindergarten and on to grade school.

When do you think is a good age for a child to start preschool?