I stand corrected. Incidently, Schnelle writes: "Language, the world of theological concepts presupposed, and the different situation point to the conclusion that I John and the Gospel are by different authors."
The gospels are tradionally dated to mid to late 1st century. They are dated by virtually all contemporary scholars (of whatever religous persuasion) to late first century, or possibly (in the case of John) very early 2nd century.
Udo Schnelle, for example, dates Mark to 70 CE, Matthew and Luke to 90 CE, and John to between 100 and 110 CE.