I live in a house that was built in 1999, this outlet currently mounts a light fixture. I want to replace the lights with a ceiling fan but I am not sure if the current outlet box will support the fan.
Sorry, but this junction box is not rated, won't support a ceiling fan. You will have to investigate further to determine how the box is mounted and replace it with a box rated for a ceiling. If you have attic access to this box, replacing it will be easier. If not, it will be more difficult and you might have to remove some of the ceiling around the box to cut it out.