What is the test for a jury to determine whether or not to consider appellant's youth in determining the reasonableness of any belief he had in the need to act in self-defense?

Assuming without deciding that the jury should have been instructed specifically to consider appellant's youth in determining the reasonableness of any belief he had in the need to act in self-defense, and also assuming the more rigorous test of prejudice from Chapman v. California (1967) 386 U.S. 18 applies, we conclude "beyond a reasonable doubt that the error complained of did not contribute to the verdict obtained." (Id. at p. 24.) Here, the jury was convinced beyond a reasonable doubt that appellant did not actually⁸

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