Contrary to what popular culture would lead us to believe, angels are not humans who have died, gone to heaven, and got retrofitted with a halo and a pair of wings. Angels are heavenly beings, created by God and completely distinct from humankind.
Though angels can appear in the form of humans, such as when three angels visited Abraham in Genesis, angels are less likely to look like this:
And are more likely to look like this (see Ezekiel 1:5-14):
Which makes the idea of cherubim guarding the entrance to Eden much more intimidating.