Muchachco is used in some localities, and by older speakers, much more than others. Likewise, English "lad" is understood by all English speakers, but used far more in the north of England than the south. It is also used more in the plural than the singular, in the armed forces, sports squads, and groups of older men who have been together since their shared youth. A "night out with the lads" could involve 20's, 30's, 40s or even older. I've not heard "laddie" outside of Scotland - it is old-fashioned and possibly patronising.