The answer appears to be in 1483, at least in the plural.
The OED gives sense 2 of the verbal noun learning five different subsenses, of which at least the last (and perhaps others; it is subclear) is marked obsolete. I include a few citations in the plural, with bold emphasis mine.
2. What is learnt or taught:
- a. a lesson, instruction;
- 1483 Caxton G. de la Tour cxxxvii. M vij, — The thre enseygnementes or lernynges whiche Cathon gaf to his sone.
- 1611 Shaks. Cymb. i. i. 43 — The king..Puts to him all the Learnings that his time Could make him the receiuer of.
- b. information or direction;
c. the ‘teaching’ of a person; a doctrine; also, a doctrine or maxim in law;
- 1549 Coverdale, etc. Erasm. Par. Rom. 34 — To expounde unknowen learnynges.
- 1560 Pilkington Aggeus C ij (Matt. xv. 9), — Teaching learninges which are the commaundementes of men.
- A. 1626 Bacon Max. & Uses Com. Law Pref. (1636) 2 — Particular and positive learnings of lawes doe easily decline from a good temper of justice.
d. a branch of learning; a science;
- 1570 Billingsley Euclid xi. xi. 315 — It is no rare thing in all learninges..to haue one thing more generall then an other.
- 1605 Bacon Adv. Learn. i. vi. §13 (1873) 49 — He did send his divine truth into the world, waited on with other learnings.
- 1613 Sir H. Finch Law (1636) 6 — The rules of Reason are of two sorts; some taken from forreigne learnings, both diuine and humane.
- e. an acquirement. Obs.
My personal impression is that the modern use sounds like annoying business jargon or non-native speaker use, and I would not use it myself.