There are no rules when it comes to makeup. Have fun. And do whatever you want. For this look i wanted to create a smokey eye but also keep it grounded - which is why i tend to always use a brown mid-tone colour in the crease of the eye. Regardless of age i tend to prefer to keep this colour matte. The rest can be shimmery and brilliant but matte colours tend to look best and most flattering in the crease of the eye.
But remember - there are no rules. Its only makeup!