I think many didn't get what Zola meant. When he meant "top clubs" he was talking about the creme de la creme of football clubs, not Fulham or Nice!
It is pretty much De Ligt at Ajax and Vinicius Junior at Real that are 18 years old starting regularly for TOP clubs. Even if there are a few more, then it doesn't negate what he said. It is not common for a 18 year old to be a first XI player for a club ACTUALLY COMPETING for trophies each and every season with great success, like Chelsea have been doing (and hopefully still will).
And please don't take this as me saying Hudson-Odoi doesn't deserve more starts because I am very frustrated with his lack of playing time.