In physics, there are two types of energy potential and kinetic.
Potential energy is just that, something that has the possibility of happening. An apple hanging from a tree, a book on a table.
Once the apple or book falls from their perch, the potential energy is transformed into kinetic energy, it is realised as movement with possibly secondary vibrations or ripples which can be felt.
In your excerpt
He was kinetic and yet totally in control.
The author is using her vocabulary of movement to describe the appearance of Prince on stage, the energy he exuded, his movements, and his dancing. She is saying he was moving quickly and energetically, but was still in control. If you've ever seen Prince perform, you will know that he is always in control.
Also with performers, they can be described as being kinetic at an energetic level. Electric might be a good synonym where the performer takes on a buzzing/humming quality with their presence, like a high voltage transformer.
Ballistic would imply a singular, sudden unidirectional movement.
Bouncing off the walls would imply movement without intent.
Neither would be appropriate for describing how Prince moves and performs.
Given I am X, what's valid for X is in almost all cases is the following:
an adjective (I am hot, I am third, I am ready)
a noun or pronoun (I am a cat, I am a worker, I am him, I am George)
a verb's present participle form, these always end in -ing (I am walking ..., I am envying ...)
a verb's past participle form if it makes sense to express a state and can also work as an adjective (I am destroyed, I am surprised)
rarely, a preposition (I am of the tribe, I am to lead my group)
any of the above with an adverb in front, (e.g. I am very X)
Adverbs can appear between I and am, like really, definitely, etc.
What X can't never be is the plain form of a verb.
So you can say I am walking but never I am walk.
You can say I am to walk but not I am walk.
You can say I am cooking hamburgers or I cook hamburgers but never I am cook hamburgers.
You also are required to express am in all the above situations. Am is not optional, but it's often said in the contracted form I'm.
Best Answer
Yes, it is grammatical, and yes it means "if I die when I am young". "If I die young" is not a sentence by itself, but would normally be the dependent clause in a conditional statement.
Die is used as a copula in the sense that it is the primary verb linking the subject and predicate, but that's a pretty simplistic sense.
'Copula' usually refers to an existential 'linking' verb like 'be' rather than an active verb like 'die'. However, if you look at this answer, you'll see that although 'die' is not normally a copula, 'die' in "I die young" fulfills many of the criteria, particularly B and E. I'm not familiar enough with copulas to say for sure whether it is or isn't, but it looks close enough to me.
'Young' could be considered an adverb describing the way you would die, or as an adjective describing yourself at the time of death. I can see arguments both ways. 'Young' is normally an adjective, but [noun][verb][adverb] is the more common pattern. If I had to choose, I would call it a predicate adjective modifying 'I', as in the sentence "I am young" (where 'am' is a copula).
Yes.