I honestly think as a child he was 10-12 years, then as an adult 17-19 years. 7 is WAY too young, why would 14 be considered an adult? That's still technically a kid.
He's 9, and when in the future, 16
It's canon, and said my Miyamoto (and source was posted three times in this thread)
And judging about that, I'd say he's about 10 in Majora's Mask
I always imagined he was 10 and 17 so I wasn't far off
I don't think the nickname "adult link" is a problem considering he was 16... in medieval times a 16 year old male would most certainly be considered a man. He could be married with children already.
18 is just the official adult age in the United States. In Japan, it's 20. It can be different in other countries, such as Hyrule. I think most people assume he's 10 in OoT.