Question regarding where to turn

My DS is nearly 3. He will be three in two months. His school is recommending that he have an evaluation and I am ok with that. They are concerned that he doesn't make much eye contact when he gets in trouble, he tries to taste the paint, polish (he is an a montessori school), and he is showing signs of aggression (scratching them) when he is asked to do something he doesn't want to do. These things have been a concern all year, but we decided to wait and see if it was because he was so young. Now at three, he is still doing it. His eye contact is better, he had stopped putting things in his mouth but has started back, and he has started being really defiant and aggressive when he doesn't get his way. Oh and they are also concerned about his lack of focus for long periods of time on lessons-long meaning 20 - 30 minutes. He did have a word explosion and now talks in sentences, communicates his needs and wants, etc. He also knows all of his ABCs, numbers, letter sounds, animals and sounds, etc. He loves playing with other children and has no problems socially. His aggression is directed at adults and not other children. He is also very implusive and will run to whatever he is interested in at the time no matter what he is doing.

 My question is where do I start if I want to have an evaluation done? Is is too late to call early intervention? Would he even qualify since he has language skills? Should I go to a developmental pediatrician?  Should I wait a little longer to see if  this is an age thing?

I would really just like to have him evaluated to make sure that everything is ok. However, since he is has met all of his developmental milestones listed for his age, I don't know who who to go to or if I should.