I didn't look at the chart--I'm too lazy--but our physician suggested that the sentences kids make should be 1-word-long per year of age for ND. So a 2yo should form 2-word sentences, and a 3yo should form 3-word sentences.
I'm not sure how soon after that the rule breaks down, but I'm betting kids don't wait for their 4th birthdays to make 4-word sentences. But that's just my guess.
Throwing a ball happens before 2. I'm pretty sure you're right about that, too. Both our kids did, and they weren't terribly advanced in the motor skills department. Certainly not DS7!
FWIW...
