O. vittatus grows to about 14", i think they can grow to that size in captive. I've kept mine from 7" to 12" in 2 years or so. But I prefer keeping these, O. waandersii. Gold body with prominent lateral line, reddish fins. They're varied between rivers/states.
This one from different river, different state but same species
As for the lemon barb, in captive they can grow up to 5kg, biggest captive I've seen, exclude the wild, can grow even bigger up to 8-10kg. So a 5kg specimen easily over 20", perhaps 26-28".