My apologies for not responding to this earlier: the month of May dealt my family devestating circumstances that we are only now beginning to recover from.
"Can you share how you are are sure that Robert Abernethy was born on or just before April 3, 1633?"
First, under the then laws of the British Government, it is clear that he was a bound servant, serving a set period of time before being a free member of the colony. In the 1650's, the laws that applied in the Virginia Colony specified the number of years to be served based upon a bondservant's age when sold into bondage [src:Abbot Emerson Smith, "Colonists in Bondage: White servitude and convict Labor in America", University of North Carolina Press, Chapel Hill, NC, 1947]. If the servant was 20 years of age or older when sold into bondage, then the length was four years. If younger, then the length was until the bondservant's age of 24 (6 years for an 18 year old, 13 years for an 11 year old, et cetera). That rule was certainly applied in other Virginia counties (although there were modifications from time to time) and there is no reason to suspect it was suspended in Charles City County. That would suggest that Robert was aged 19 in when sold into bondservice on these shores. We also know when his name appears on a headright land grant to Robert West, who paid his passage across the Atlantic to the Virginia Colony [src: Library of Virginia website: Land Grants].
British bondservants were forbidden to marry until after they completed servitude. Until then they were little better than slaves except that eventually they would be freed. Robert Abernathy / Abernethy served as an agricultural bondservant in the Virginia colony of Charles City from 1652 to 1657. While we do not know the exact date his services were sold, it may be assumed that it was very soon, perhaps mere days, after Robert West's ship arrived. It took time for one who imported servants to apply for a headright grant, and it probably also took considerable time before such a grant was issued. Fact: the West headright grant with Robert's name on it was dated 2 Aug 1652. [src: Virginia Land Grants, 1600-1800, Lib of VA website].
Thus, we can determine that his age was 19 when he was sold into agricultural bondservice before he could become a free citizen and able to marry.
There is a court document [src: Charles City County Court Order Book, 1655-1658, LDS Call #30989, 30990, p. 98] that is dated 3 Apr 1657 and was actually entered into Charles City County Court Records later in April (the 25th) of that year. That court order is significant for several reasons, not the least of which is to pinpoint his birth year. It helped establish a precedent in Colonial law for women to own property in their own names, apart from thier husband or father, as could be the case in Scottish law but not English. Heretofore, a woman's property became vested in her husband at the moment of her marriage. This court order helped start the process of woman's emancipation in America from those restrictive laws, while women in Britain still suffered under them until the 1860's. Scottish legal practices allowed women to hold property in their own name while English laws even into the 1860's required that all property due to a woman became, upon the instance of her marriage, the sole property of her husband to dispose of as he wished. Also, Scottish laws allowed for the legitimation of a child born out of wedlock, which took much longer to obtain in Britain itself.
In that document it seems clear that Robert was ensuring that the daughter of Sarah Cubisha, his "now wife" (and possibly Robert's biological child) would have a dower when she became old enough to marry. Women in the United States may now hold property in their name alone, thanks in part to that document of 3 Apr 1657. It also proved that on that date Robert Abernethy and Sarah Cubisha _were_ married (probably the very first thing they did when he became free). It also showed that neither were sufficiently literate to be able to sign their own names, which put a final and definitive nail into demolishing the beguiling theory of his presumed heirship to a Scots Barony.
Robert's birthdate was therefore no _later_ than 3 Apr 1633, and may have been a day or two before but was certainly not months (or even weeks) earlier.
"Also can you share why you think he was from the lowlands rather than the highlands?"
We do not _know_ where in Scotland Robert came from, only where some individuals _thought_ he may have been from. But the chance that it was from the lowlands is just as possible as from the highlands or midlands, and I would be remiss as a serious genealogist to be unduly influenced by a theory, however beguiling, that cannot be demonstrated from existing documents.
When the religious leaders of Scotland over-ruled the Military leaders of the Scottish Army that Sunday, they squandered a final chance to alter forever the history of the British Isles and win Scottish independence from Britain. And foolishly threw away the lives of tens of thousands of Scots soldiers (see http://www.scotwars.com/html/battle_of_dunbar.htm)http://www.scotwars.com/html/battle_of_dunbar.htm). The disastrous defeat of the Scottish Army at the Battle of Dunbar in Sep of 1650 had all but wiped out the rank and file of an Army that came mostly from the rugged Highlands. The hastily assembled Scottish Regiments that fought at the Battle of Worcester came from such Highland areas as Inverness, Ross, Nairn, Caithness, Uist in the Orkneys, the Outer Hebrides, and Skye. Then there were many regiments from the fringes of the Highlands, south and east of the Grampian Mountains: from Angus, Aberndeen, Banff, Fife, Kincardine and Perth; there were regiments drawn from the midlands: Clydesdale, Stirling, Glasgow, Ayrshire. And the lowlands: Teviot, Eskdale, Berwickshire, Peebles, Renfrew, Selkirk and Dunbarton. The DNA evidence we have accumulated in the past 4 years indicates that Robert's origin in midland to lowland areas is at _least_ as plausable as an origin from the wilder highland areas. And Robert's name is _not_ on the List of the POW's in the custody of Cromwell's forces as of the 9th of Sep 1651 after the Battle of Worcester.
While myth has provided a charming scenario of aristocratic origin for our Robert, the documentary facts so far belie the possibility that he was an educated officer in that Battle at Worcester. Lowland origin is likely and should, indeed, must be considered.
Alas, wishful thinking has long painted an untrue picture of native American Indian women as Princesses and many European men as descendants of aristocratic or royalty when such an enticing theory very often simply cannot be substantiated. Beware wishful thinking that flies in the face of factual evidence.