Our DS7 was severely delayed in speech. At 18 months he wouldn't talk, wouldn't react to his name and did not seem to understand anything we were saying to him. I had him evaluated at that point and the results were that he was up to 70% delayed in speech (he was at a 6-9 month old level). He didn't really speak sentences until he was almost 3, but he was counting objects and knew letters and numbers before he was 2. He has told us that he remembers when he was very young he couldn't understand what we were saying to him, it just sounded gibberish.
He's always been a kid who just kind of gets stuff overnight. That was the case with walking, reading, math, any skill set for that matter. He wouldn't know or do anything and basically mastered it overnight just because he felt like it.
Fast forward: at age 6 we had him tested because we had a lot of question marks about his uneven development, emotional issues and some concerns from school as well. At that time his verbal IQ came back at 99,8 percentile. So go figure. He does like to talk a lot though. He can start a conversation with anybody, anytime, anywhere...