I have heard from more than one person that adults with Down syndrome have the minds and abilities of "a 12 year old".
Well, this is NOT the case.
Down Syndrome Fact of the Day #26:
Children with Down syndrome do NOT “plateau”.
Each person with Down syndrome has his or her own talents and unique capabilities, and it is important recognize these and reinforce them. Learning is a lifelong experience for people with Down syndrome, just like everyone. Individuals with Down syndrome do in fact learn at a slower pace but nonetheless, continue to learn throughout their lifespan.