People can make this subject intricate as they want. During colonial times Don and Doña were strictly reserved for those in the public eye. I say this because you will notice as you research, ecclesiastical individuals use it, government officials, landowners and nobility. These were not only Spanish, but could be a cacique or any native that also held similar status or position. It's closest equivalent in English would be Lord/Lady. However, in the Spanish-speaking world it did not always denote nobility, although it certainly could.

There was once instance, I read a child in my Villaseñor line baptized as Don and he was five days old. I had never seen anything like it!