。
In short, he gets bored of everything.
Literal
Essentially he [topic-は] anything [to-にでも] tires-of-[explanatory-のだ].
飽きる ('to tire of / become bored with') takes に for what one tires of. にでも is particle stacking (に + でも, 'even to') giving 'tires of anything at all.' のだ frames it as the underlying explanation.