As conjunctions, although and though are interchaneable, with although appearing more frequently at the start of sentences and to some ears sounding more formal, and though appearing more frequently within sentences. Although I am old, I still have energy and Though I am old, I still have energy are both acceptable in formal and informal writing.
Only though can act as adverb after a verb—a distinction few, if any, mistake: I said I wouldn’t make it; I did, though.