Question: Is it a sound idea to start off a novel with an event then flash forward several years?
If it is, is here a reliable way of showing that a significant amount of time has past without putting "ten years later..." at the top of the new chapter?Answer:
Beginning with a prologue which happens years before the main character enters the story is a fairly common device. Often the event in the prologue is the inciting incident of the story.
You can just call the first chapter, "Prologue," and the next "Chapter One." The change to the main character's point of view should be obvious as well.
Some people frown on prologues, preferring to start with the main character so the reader can establish an immediate connection. However, as with any guideline, it's really up to you. Whether it works depends on your story and what other redeeming features your storytelling offers.
Trust your feeling, unless and until you come up with an idea that feels better and/or you get a lot of negative feedback.