Very impressive no doubt, and again, they are brothers, so genetics plays a part. But their achievements aren't even close.
His (younger) brother, Nigel achieved two bronze medals (placing 132nd and 114th overall) at the age of 15 and 16 [0]. Quite good, specially at a younger age than most participants.
Terence [1] got a gold medal (13th place) right before completing 13 years of age. He achieved a similar feat (28th place) around his 12th birthday and a more humble performance (87th place, but still better than his brother's best) around his 11th birthday. At 11, better than 58% of his competition, some of the best 17 and 18 year olds at competitive math in the world.
He is cited as "the youngest bronze, silver, and gold medalist, respectively, in IMO history." [2]
If I were to guess, his brothers and parents pushed him, and had more experience with teaching compared to their older son. They got him interested, and he went from there.
He was probably lucky to be the younger brother growing up.
Oh, then I was completely wrong :D I would think the youngest kids are generally the more academically advanced. (But this is coming from someone who has 0 kids :D)
His (younger) brother, Nigel achieved two bronze medals (placing 132nd and 114th overall) at the age of 15 and 16 [0]. Quite good, specially at a younger age than most participants.
Terence [1] got a gold medal (13th place) right before completing 13 years of age. He achieved a similar feat (28th place) around his 12th birthday and a more humble performance (87th place, but still better than his brother's best) around his 11th birthday. At 11, better than 58% of his competition, some of the best 17 and 18 year olds at competitive math in the world.
He is cited as "the youngest bronze, silver, and gold medalist, respectively, in IMO history." [2]
These are entirely different levels.
[0] https://www.imo-official.org/participant_r.aspx?id=783
[1] https://www.imo-official.org/participant_r.aspx?id=1581
[2] https://en.wikipedia.org/wiki/List_of_International_Mathemat...