The date of Arador's birth appears only in The History of Middle-earth volume XII, The Peoples of Middle-earth. It cannot therefore be considered completely reliable.
2
As for all the later Kings of Arthedain and Chieftains of the Dúnedain, the 'Ar(a)-' element of Arador's name means 'royal' or 'kingly', and relates to their descent from Isildur. The '-dor' part of his name, however, is problematic: it might relate to the common (n)dor 'land', or it might be a variation of taur, in the sense of a royal or noble title, or of a forest. Since it is known that not all of Aragorn's descendants had interpretable names, it is also perfectly possible that the second part of Arador's name is not intended to carry a specific meaning.