I know I can write an epilogue, but are there other options?
Denouement
Traditionally this character wrap-up happens in a novel's denouement.
19th Century authors could go overboard with the long explanation on every character's eventual fate, but this matched the (hanging) story threads. Jane Austen has massive info-dumps at the end of all her novels, but her stories have an extreme number of characters each with their own trajectory – she's also skilled at twisting dry information into ironic humor, and we get to know these characters first so her denouements are entertaining.
(Austen's also shuffling everyone's character relationships right up to the climax so the denouement is the only way to tell us how everyone fared in their final situation – it's not just a bow on the end, there's still new information we want to know.)
"And they lived happily ever-after," is also a traditional denouement just very brief and on-the-nose.
My point is a denouement is flexible, but there needs to be a compelling reason to keep reading.
Flash Forward
No need to over-think it. The 'leap' here is simply that your final chapter/scene takes place many years/decades later.
Readers don't need an explanation. Your story already has methods for establishing time and place for each scene. This is simply another scene, with cues woven into the prose to show how much time has passed.
Frame Story
A frame story is a second narrative outside the main story. The cliche is rigid 'bookends' with an opening scene and a closing scene – reducing the main story to a 'flashback'. But there are more creative ways to interweave a frame story so it appears more like a dual narrative, or where the two stories appear to blur/align, or one changes the direction of the other.
Your narrator-as-author could be the frame story, but it will need more than a reveal ("...and Dear Reader, I was that little girl!") to be a compelling 2nd narrative with its own conflicts and characters that somehow still relate to the 1st.
(For instance, the film Titanic has a frame story which doesn't add new information, but helps ground the main story as 'historic reality' – in contrast to it actually being fictional melodrama.)
Epilogue
I think an epilogue is appropriate when the perspective shifts completely.
An example might be a new character who has just read the authors' book, and wonders how much of that story was true since the author would have fabricated details they could not have known. This character could attempt to research what became of these people, perhaps specifically to find answers that are not in the book, and discover the author must have been that child in the novel.
This 'perspective shift' allows for character resolutions that would have been unknown to the narrator at the time of writing, and also the extreme shift of having the story continue after the original narrator's death. It also allows for an ambiguous resolution where the researcher can't be sure of what really happened, and the possibility of contradicting the original narrator.
Cut It
Hard to let go of our babies. Beta-readers or an editor might have a better perspective whether the epilogue is contributing to the novel, or tacked-on for the sake of completion.