My nephew didn't speak until he was well past his 3rd birthday. Once he started, and he did indeed come out with complete sentences, my brother showed him some photographs of elderly relatives he hadn't seen for quite some months and he could tell him all of their names.
Inigo understands pretty much all of what is said to him. A couple of days ago, whilst watching television, he was occupying a chair that I wanted to sit in. I said "Inigo, would you like to sit on my knee?" and without taking his eyes off the screen he stood up and when I sat down he lifted his arms to be picked up and plonked down again. He also reacts very sensibly to "I'm about to put the food on the table," rushing into the dining room and climbing up into his elevated seat. He tries to fasten the lap belt, but hasn't got the hang of it yet.