Guardian angels are only given if you are very holy and divine. If you are not, then none will be assigned to you.
Guardian angels are assigned by God and God only, not if you ask personally for one. You need to pray to God for help and if help is granted then, he will assign an angels to you.
From my experience Derek Prince was correct in his thinking, that archangels are only assigned to God, but guardian angels are assigned to people.
Guardian angels are generally 5'6" feet in stature and they can be male or female. Generally you have to be very sick to be granted a guardian angel. These angels (of which there are two) rarely leaves your side and if you need assistance, you ask your guardian angels for help. God will grant your angels even more strength to assist you in your day. In 2011 because of my torment by demons I was assigned a guardian angel and she's never left my side. Since then I was granted more angels.
Guardian angels in a way are a gift from God and are always there to provide a resting place for you.