Should this go in "flirting" or "sports"?
Glad I'm not the only person who had that thought, even if most wouldn't break into a rendition of Olivia Newton-John's "Physical"
Can physique mean fit?
No, I would use «être en forme».
I guess this means he wants to work out to build up some muscle... Anyone can confirm?
So could active be a translation?
That's not the meaning that I immediately thought of... but I suppose you could call it "working out" :-)
Could the sentence as written also refer to wanting to be in better shape? With "plus physique" meaning more along the lines of "better physical condition"?
No, "physique" is not used with that meaning in French.
To be "more physical" is a common colloquialism to be more aggressive/assertive in a sport. Does this sentence mean to do more athletic activities in general?
Actually this sentence, in isolation, is not very clear.
But "être physique" can refer to sports (le rugby est un sport très physique) or to players (aggressive)
Could it be said by a ghost expressing its desire for a material body?
...Or by a piece of language learning software that has achieved a level of such complexity that it now stands upon the precipice of full blown sentience
Skynet begins here :)