It is not possible to fit the Sports Jacket into an exact era.
The word "Sport" was applied to any informal clothing.
The Norfolk Jacket of Edwardian years was I suppose the first Sports Jacket.The classic cut tweed Sports Jacket appears occasionally in studio photographs during the late twenties becoming totally acceptable by the early thirties.
The informality of his checked jacket, checked shirt, checked woollen tie and V necked pullover would not have been "good taste" at an earlier date. Here it is the height of fashion.
Note that once it has been tucked into the V neck the necktie is tugged forward slightly.
Above photograph: Alexander Studio Southampton Violet date : 28 Jan 1935
Date 1935: Age about 18 years old Estimate: born 1917 ± 3 years