All of the angels were created in the beginning when God created the world. They are purely spirit, without a body and are immortal so they never experience death.
Humans are made of flesh and soul and are mortal so we experience death. Our souls are immortal but not the same substance as angels.
When someone dies, they will become a saint in heaven (provided they are free from sin), not an angel. Many, during grief of the death of a loved one, may say that that loved one is a guardian angel now or an angel in heaven, but this is not true. Although we need to be sensitive of the grief of the loved ones left behind, we also need to help others understand, after the grief, that people become saints not angels.
When we die, we don’t become an angel, we become a saint!
We can still pray to our loved ones and ask for their intercessory prayers for us. There is nothing wrong with doing that. We would’ve asked them to pray for us when they were on earth. They are saints in heaven and saints can offer prayers for us to God’s throne. That’s a loving thing for them to do for us. I have asked for my grandparents and godparents to pray for me. Think of all the people you have known that died…they could be praying for you. That could be quite an army of saints! Picture them with armloads of prayers laid at the foot of God, all for you.
A good article for you to check out on this subject is http://littlecatholicbubble.blogspot.com/2014/03/humans-never-become-angels.html