Disparity of force is a factor. If one is attacked by a gang, of any age, the disparity of force would be justification if you feared for your life or great bodily harm. So I just do not worry about such things in any state I go to.
I do not think this is true in California. The fear must be the fear a reasonable person would feel in similar situation. The jury will decide if the fear reached that level. As pointed out, a different decision is most likely in San Francisco than in Dallas under similar conditions.