Beat me to it! 
On a sort-of related note, there’d also been some doubt in the sixteenth century as to whether Queen Mary could have the same powers as a King (because she was the first ever Queen Regnant):
[QUOTE=Queen Regent’s Prerogative Act 1554]
An Acte declaring that the Regall Power of this Realme is in the Quenes Majestie as fully and absolutely as ever it was in any of her moste noble Progenitours Kinges of this Realme.
FORASMUCHE as the Imperiall Crowne of this Realme, withe all Dignities Honours Prerogatives Aucthorities Jurisdictions and Preheminences therunto annexed united and belonging, by the Dyvine Providence of Almighty God, ye most lawfully justly and rightfully discended and comme unto the Quenes Highnes that now ys, being the verye true and undoubted heire and inheritrixe therof, and invested in her most Royall Person, according unto the Lawes of this Realme; And by force and vertue of the same, all Regall Power Dignitie Honour Aucthoritie Prerogative Preheminence and Jurisdictions dothe apperteine, and of right out to apperteine and belong unto her Highnes, as to the Sovereine supreme Governour and Quene of this Realme and the Dominions therof, in as full large and ample maner as it hathe done heretofore to any other her most noble Progenitours Kinges of this Realme: Nevertheles the most auncient Statutes of this Realme being made by Kinges then reigning, doo not onely attribute and referre all Prerogative Preheminence Power and Jurisdiction Roiall unto the name of King, but also doo gyve assigne and appointe the Correccion and Punishment of all Offendours agaynst the Regaltie and Dignitie of the Crowne and the Lawes of this Realme unto the Kinge; By occasion wherof the malitious and ignorant persones may bee hereafter induced and perswaded unto this errour and folly, to thinck that her Hignes coulde ne shoulde have enjoye and use such lyke Royall Aucthoritie Power Preheminence Prerogative and Jurisdiccion, nor doo ne execute and use all thinges concerning the sayd Statutes, and take the benefit and privilege of the same, nor correcte and punishe Offendours against her most Royall Person and the Regaltie and Dignitie of the Crowne of this Realme and the Dominions thereof, as the Kinges of this Realme her most noble Progenitours have heretofore doon enjoied used and exersised:
For thavoiding and clere extinguishment of whiche sayd errour or doubte, and for a playn declaracion of the Lawes of this Realme in that behalf;
Be it declared and enacted by thauctorite of this presente Parliament, that the Lawe of this Realme is and ever hathe been and ought to bee understande, that the Kinglye or Regall Office of the Realme, and all Dignities Prerogative Royall Power Preheminences Privilegies Aucthorities and Jurisdiccions therunto annexed united or belonging, being invested either in Male or Female, are and bee and ought to bee as fully wholly absolutely and [enteerly] demed judged accepted invested and taken in thone as in thother; so that what or whansoever Statute or Law doothe lymitte and appointe that the King of this Realme may or shall have execute and doo any thing as King, or dothe geve any profitt or commodite to the King, or dothe lymitte or appointe any paines or punishement for the Correction of Offendours or Transgressoures against the Regaltie and Dignitie of the King or of the Crowne, The same the Quene, (being supreme Governesse possessour and enheritour to the Imperiall Crowne of this Realme as our sayd Sovereigne Ladye the Quene most justly presentlye is,) may by the same aucthoritie and power likewise have exersice execute punishe correcte and doo, to all intentes construccions and purposes without Doubte Ambiguitie Scruple or Question: Any Custome Use or Scruple or any other thing whatsoever to be made to the contrary notwithstanding.
[/QUOTE]
The above wasn’t repealed until 1969! 
You say that, but in French law the first-born twin was (is?) considered to be the younger of the two. This was an application of the principle “first in, last out”! 