That is a nice one, I have that variety and it is the only one that keeps its variegation when in full sun. Has it bloomed, it should have white flowers. Probably not three years old, most likely a one year old rooted cutting. As MichaelS said, it needs to be thinned out. Serissa can be wired anytime. If it were mine, I would decide which branches I wanted to keep, trim the rest off (make sure to strike the cuttings, they root easily) and then wire for shape.
I don't know how cold it gets for you in winter, so it might need to come inside. Serissa are subtropical, not tropical and I find that they do better if they get exposed to a little chill. The ones that I have in pots stay outside unless it is gonna get below 35 F.
Hope it helps,
John