I don't believe it's guaranteed.
If they are hot young, they are more likely to be hot when older.
If they are shy, skittish and piss themselves when young, they are more likely to be that way when older.
None of the above is a guarantee and there are exceptions and rules and there are rules to the exceptions.

Me personally? I like a laid back pup that has a "calm" about him and a relaxed confident calm in his eyes - along with smarts. I also like some fire. For breeding good bulldogs - I like having both on my yard.