The problem lies in the fact that nothing apart from the deeds of the great and good (or otherwise) among the monarchy, aristocracy and Church was recorded in any enduring form until about 1430. One of the earliest written records of life in the lowerarchy involves mention of morris i.e. it is older than written record.
There are several theories, it may have been named from the Latin (mores est = it is the custom) so could date back to Roman times. It was certainly a court entertainment in the time of Elizabeth 1 (for the Scots, yes, I know the current one is Liz One to you!). There is even a fairly ludicrous theory that it was invented in Spain by John of Gaunt and his men based on the Basque dancing (same root as the "moorish" idea) with the intention of providing court entertainment at some banquet or other.
The strength of its links and similarities with pagan (i.e. rural and pre-Christian) symbolism across Europe suggests it is much older and more "of the people" than some Tudor court entertainment.