Originally, I was going to say that Link going back in time as an adult in OoT is a red herring since anything could create a scenario in which Link fails, but I think I might have come up with a better way to explain things instead.
A) There are two types of time to think about here. "Hyrule" time, and "Link" time. In a traditional time travel story, you generally deal with "Hyrule" time. This is the timeline for an entire universe. One timeline with various pasts/presents/futures to visit.
B) "Link" time is someone's *personal* timeline, and can exist in multiple "Hyrule" times if someone is traveling between them. At the end of OoT, Zelda sends Link back in time to when he was a child, but this is in terms of "Link" time. She simply rewinds his "personal" time if that makes any sense. The timeline which Ocarina (almost entirely) takes place in, remains intact. This rewinding does create a separate "Hyrule" timeline.
C) Now there's nothing in OoT to imply that Link going back as an adult is time travel in a universal or personal sense, but if it is in terms of "Link" time, it would explain how a new timeline is created. However, this does produce questions. If it is travel along "Link" time, then why isn't Link frozen in time when he returns to the moment he pulls the Master Sword? And is it even possible to move forward in "Link" time this way? Questions, but not unanswerable ones.
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This is Yesmar.