People in the 14-17 group of age were most affected by the changes.
I know, this seems to make sense, and your meaning is clear, but if you want a high score for vocabulary you need to use better collocation inside your noun phrases:
The following are all possible. Unfortunately you just have to memorise them. Try to use them as soon as possible in your writing practice and soon they will become automatic.
More often in IELTS, ‘person’ is plural (= ‘people’), and so these noun phrases are also possible:
Of course we could be more specific about ‘person’ or ‘people’: