Why does The Odyssey start out with Telemachus' journeys instead of his father's?

The first four books of The Odyssey are known as the "Telemachy," as they introduce us to the voyage of Odysseus' adolescent son, Telemachus. Why do you think that The Odyssey begins with this story, and what are the most important things that we learn about Telemachus?

I believe the book starts off this way because Telemachus has to find his father, Odysseus, for whom this book is written for. Odysseus has to come back some how, and since he seems to be caught under some sort of love enchantment/spell with the nymph, Calypso, I don't think he will be completely available to continue the rest of his Kleos and then his Nostos without being given a small bit of assistance. Aside from this, we learn more about Telemachus and his personality. He is a young adult, who has yet to recognize it. He is constantly degrading himself and throwing mini- tantrums when he is in any sort of dilemma or something doesn't go his way. Now, these actions aren't very surprising coming from the spoiled, rich, and slightly bratty child of the Queen and King figure of an entire city in Ancient Greece. Having read this much about Telemachus and his few encounters with people outside of his palace back home  makes me wonder about how long he may last during his  journey to rescue his father.