it takes about 2 to 3 months for the guppy fry to look like a adult
I'm guessing 4-5 months!
If by adult size you mean 'mature enough to breed' then they do that in 1 or 2 years and can breed at a couple of inches long. If you mean 'fully grown' Goldfish continue growing for their whole life...
They can be fully grown at 12 to 14 weeks if they are given good conditions.
like 6 weeks