Unless you see physical signs that he's going through early puberty such as body odor, hair, big spurt in height, etc., I think it's pretty safe to assume this isn't puberty.
When girls approach puberty they often become very moody and unpredictable, but that's not usually the case for boys.
I agree with Margy and think you need to look elsewhere for this sudden negative turn in his personality.
Could he have learned the shouting and swearing form anyone , children do learn from what they see and hear ?