A hobbledehoy is a clumsy or awkward youth.
You will not find a better description of the type than in Anthony Trollope’s The Small House at Allington: “Such young men are often awkward, ungainly, and not yet formed in their gait; they straggle with their limbs, and are shy; words do not come to them with ease, when words are required, among any but their accustomed associates. Social meetings are periods of penance to them, and any appearance in public will unnerve them. They go much about alone, and blush when women speak to them. In truth, they are not as yet men, whatever the number may be of their years; and, as they are no longer boys, the world has found for them the ungraceful name of hobbledehoy”.
But where the world found it is far from clear. The word seems to have been around at least since the sixteenth century, but was long distinguished by seeming never to be written the same way twice. It may well be related to Hoberdidance or Hobbididance, which was the name of a malevolent sprite associated with the Morris dance (and whose name is from Hob, an old name for the Devil; nothing to do with hobbits). It may also be linked to hobidy-booby, an old English dialect word for a scarecrow. The modern spelling seems to be the result of popular etymology, which has changed a puzzling word into something that looks as though it might make more sense.