My Dd1 is still only 5, so may turn out to be distinctly average yet, but she always did things early - crawling, talking etc etc with the exception of walking (That was fully walking by 13 months, very average I think).
I noticed however, when DD1 was 2 years 9 months, I was having a scan for my second baby and DD1 sat down and picked up a book about clocks. She looked at the book and said 'one o'clock', turned the page and said 'two o'clock' and so on! I never knew she could tell the time (to the nearest hour). We tested her out with a clock and sure enough no matter what time we turned it to, she could tell the hour. I checked that my mum hadn't taught her, or the nursery - and no, she just seemed to have learnt it (although she did have an obsession with clocks mind!). She's five now and in reception, and is now 'learning' it all again in class, despite the fact that she has been telling the time for about a year though.
I don't know if she is G&T though, I know she gets pulled out of class for extension reading and at parents' evening, the teachers said she was "very bright" but I have no idea how she compares to other children because she is the eldest and so I've not got anyone else to compare her with (I could speak to mums in real life in case it looked like boasting - on here, I'm anonymous!)