20 year rule for them stopping. Here's some recent but older than 20 years coat of arms:

https://commons.wikimedia.org/wiki/File:Coat_of_Arms_of_Charles,_Prince_of_Wales.svg

https://commons.wikimedia.org/wiki/File:John_paul_2_coa.svg

It is true that arms have become rather less serious business. In England the Court of Chivalry (which ultimately regulates such matters) last sat in 1954 and prior to that hadn't done so in over a century. For an idea of how big a deal this was in its day a 14th century case between Sir Richard le Scrope and Sir Robert Grosvenor lasted 5 years and involved 414 witnesses two of whom were over 100 (Sir John de Sully and Sir John Chydioke).

That said while the court was in decline the number of coats of arms being issued actually increased so make of that what you will.

First coats of arms appear in the 12th century. That didn't however stop people claiming older origins. There was a case where one side claimed that his family had had the arms in question since arriving with William the Conqueror and the other claimed to have them from a pre-conquest Cornwall. Given that both claims were obviously false its probably for the best that the case ended in a draw with both sides allowed to continue using the arms in question.

Somewhat related seals in the form of signet rings re-appeared on a large scale in the 13th century probably due to the growth in trade and written contracts.