Age for diagnosis?

Hi, i am new here and this is my first post. I have a son who will be 3 in 2 weeks and we are going through the process of having him assessd for ASD at the moment. He was seen by the community peadiatrician 2 weeks ago and she did a bit of assessment with him and said it looks likely he is on the autistic spectrum and has sensory issues but sad he is very young for diagnosis as some of the signs he shows may improve as his speech develops. She is now reffering him to her senior but said he is still very young for diagnosis? Is that right? It seems to vary in different areas. How old were you or your child when diagnosed? I had a report sent from speech and language after the two appointments he had with them, 1 at the clinic and 1 at home. Speech and language will be working with him in the school nursery when he starts next week and also the educational phscologist. His behaviour is VERY challenging at times, especially when out and about and i feel if he had a diagnosis i would be able to cope with things better as i could say to people 'he has a diagnosis of x, y or z. But at the moment people stare as they think my son is badly behaved and we are bad parents and it winds me up so much.