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Clarification: Future Trunks and Gofrain are the same age.

While traveling to ensure everything was in order, his time-travel equipment was sabotaged, forcing him into a dangerous crash landing on Earth in this timeline, near Capsule Corp. As a result, he lost much of his memory, including where he came from and how he got there.

Trunks wasn't even planned? Well, guess... but guess (Mai Trick) (Joke, not a chance, obviously). Gofrain ended up in this timeline because he was part of the Time Patrol (a
*Dragon Ball Xenoverse* reference).