Is this even limited to the 18th century, to the nobility, or to the Anglophone world?  I quote:
Sometime near the end of 1640 or the beginning of 1641 Van Vliet concluded his studies and, as befitted a fashionable young gentleman, subsequently embarked on his grand tour.
Cornelis Dekker, The Origins of Old Germanic Studies in the Low Countries (Leiden: Brill, 1999), p.63
Which refers to it as a common practice of the Dutch middle classes in the 17th century, which is something one would never guess from the current article... —  Talk