Let’s properly distinguish between SSRI’s for children, on the one hand, and SSRI’s for adults, on the other.
I have personal experience with the almost miraculous benefits of SSRI’s for adults who are severely depressed. Now, if you want to argue that the benefits do not justify the risk of side effects ... tell that to someone who has been saved from emotional misery, and possibly suicide, by these drugs.
Look up serotonin syndrome. It's not age specific from what I have read in the professional literature. I'm a doc with an interest in adverse drug reactions. Beware of what you find on the net. I'm glad you had good results. Not everyone does.