Sentence:  This had given him the strength to leave cadet school at seventeen and volunteer for active service, reach the rank of second lieutenant no later than his <WSD>hothouse</WSD>-bred contemporaries, begin his military studies in the General Staff Academy itself, and, still only twenty-five, graduate not only with top marks but with promotion out of turn for special excellence in military science. 
Meaning of the word marked with <WSD> tags:  An environment in which growth or development is encouraged naturally or artificially; a hotbed.