Is my jade plant rotting?
I really can't tell. It is browning from the base up, and I can't think of any other explanation. However, its leaves look green and firm and the trunk is firm as well. I don't think I have been watering it too much because I've watered it maybe once every two weeks or so. Another reason I was afraid of rot was because I've seen little black gnats flying around my room, and sources on the internet have said that they could be a cause. I also took my plant out of its pot to check its roots directly, and they looked perfectly normal.
Is it just coming of age? I know the pictures of jade plants I see have brown, bark-like trunks. Is that what's happening to it?