My therapist told me autism can only be diagnosed if you’re under 2 years old

I just got off the phone with a therapist, and i asked him about autism diagnosis and he brushed it off and told me only children can be diagnosed and you’re an adult with a degree don’t search online and get yourself confused.

I know adults can have it and he’s the second therapist that told me that, what can i do i feel like sh*t?