I know because his reception teacher mentioned it at parents' evening - no one has mentioned it since, but I assume he still is.
not necessarily
It is quite often the top 10% of a cohort, and obviously, children develop at different rates, and someone in the top 10% one year is not necessarily in the top 10% another year.
You also have to keep in mind that what the label means is extra monitoring by staff, so extra paper work and time.
It doesn't mean extra education, as you can give stretch and challenge tasks to anyone at all, at any time, they do not have to be on any formal list.
Quite often, the criteria for such lists are odd, for example, free school meals, pp, or uneducated parents, or less educated parents. One school I worked in the list was entirely self referred. In another school, every single child was registered on the government list as soon as they reached 16, as it made A level resources cheaper.
Also, any child could be added by any teacher, at any time, for anything, but this did last 3 years, and cross all subjects, so cause unnecessary paper work, and difficult monitoring for other teachers too, for example a friend of mine who was a maths teacher used to be pulling his hair out with students listed as "gifted" for cookery or dance, because they would show up on his register as gifted too, and had to be monitored separately.
By the age of 18 it no longer has any meaning, anyway