I've got three likely gifted boys who would test just like your son. Especially my oldest. In fact, I'm on the phone all day today trying to get some answers about gifted programs for him now that he's in 1st grade.
I think I agree with the other responders. Asynchronous development means that he may have the brain of a 4 year old, but you have to remember, even when he uses big words, that he's still only 2!!! TWO!!! How little is two?? so so little!
The best thing I did was practically home schooling. While I wanted my son to have social interaction, he didn't need preschool for the school part. We make lots of trips to the library. I let him pick the books. He used to get all non-fiction when he was your son's age. We'd almost have "units' where he'd get 3 books about polar bears and we'd read them over and over. The next week, he'd get penguins. The week after that, he'd want volcanoes. He was using words like "dormant" and "seismic" at age 3, and could describe the water cycle and the difference between lava and magma. And he ate it up. That's all he needed to keep his mind occupied. We'd also watch PBS specials together. Two very memorable ones were about the Mars Rover and one about Polio. That last one prompted a discussion and internet search for images of bacteria and viruses, as well as a discussion of the immune system.
And the whole time you're doing these things together, he's with Mommy, so he's getting the mental stimulation he needs and the emotional security he needs to grow up healthy and brainy!
It also gets your family into a lifestyle of learning. My husband calls us a bunch of nerds because we don't just go on a walk, we discuss the ecosystem and different plant species that we pass. It's usually directed by our kids, who ask questions constantly. it can be frustrating to keep up with them and always be talking, but it's also hugely rewarding. Don't be afraid to say, "I don't know, we should look that up" if he stumps you.
And be prepared to explain how vaccines work, why the earth rotates, and the atomic theory. I've done all of those with my 6 and 4 year old (and some of this while they were younger!)