Question: What is the birth date of the person who won his first Formula One victory at the 1968 British Grand Prix? 

Context paragraphs:
2014 British Grand Prix: The 2014 British Grand Prix (formally the 2014 Formula 1 Santander British Grand Prix) was a Formula One motor race held on 6 July 2014 at the Silverstone Circuit in Silverstone, United Kingdom.  It was the ninth round of the 2014 Formula One season, and the 69th British Grand Prix.  The 52-lap race was won by Lewis Hamilton for the Mercedes team, from a sixth position start; the lowest position he has ever won from.  Valtteri Bottas finished second in a Williams car, with Daniel Ricciardo third for the Red Bull Racing team.  This race was the first to be red-flagged on lap one since the 2000 Monaco Grand Prix.

2017 British Grand Prix: The 2017 British Grand Prix (formally known as the 2017 Formula 1 Rolex British Grand Prix) was a Formula One motor race that took place on 16 July 2017 at the Silverstone Circuit in Silverstone, United Kingdom.  This race was the seventy-second running of the British Grand Prix—the first having been held in 1926—and the tenth round of the 2017 Formula One season.  The race marked the fifty-second time that the race has been held at the Silverstone Circuit since the Formula One series inception in .

2016 British Grand Prix: The 2016 British Grand Prix (formally known as the 2016 Formula 1 British Grand Prix) was a Formula One motor race that was held on 10 July 2016 at the Silverstone Circuit in Silverstone, United Kingdom.  This race was the seventy-first running of the British Grand Prix, the first having been held in 1926, and was the tenth round of the 2016 Formula One season and the fifty-second time that the race was held at the Silverstone Circuit since the Formula One series inception in .

John Taylor (racing driver): John Malcolm Taylor (23 March 1933 – 8 September 1966) was a racing driver from England.  He participated in five World Championship Formula One Grands Prix, and also participated in several non-championship Formula One races.  His Formula One debut was on 11 July 1964, at the British Grand Prix at Brands Hatch driving a one-litre, 4-cylinder, Cooper–Ford T73, where he finished fourteenth, 24 laps down, after an extended pit–stop due to a gearbox problem.  Taylor did not compete in the Formula One World Championship in 1965, but continued to drive in non–championship races.  He returned to Grand Prix racing in 1966 driving a two-litre Brabham–BRM for privateer David Bridges.  His first race that season was the French Grand Prix at Reims where he scored his one championship point.  There followed eighth places at both the British Grand Prix at Brands Hatch and the Dutch Grand Prix at Zandvoort.

1986 British Grand Prix: The 1986 British Grand Prix (formally the XXXIX Shell Oils British Grand Prix) was a Formula One motor race held at Brands Hatch on 13 July 1986.  It was the ninth race of the 1986 Formula One season.  It was the last Formula One race held at Brands Hatch, from 1987 onwards all British Grand Prix would be held at Silverstone.

1968 British Grand Prix: The 1968 British Grand Prix was a Formula One motor race held at the Brands Hatch Circuit on 20 July 1968.  It was race 7 of 12 in both the 1968 World Championship of Drivers and the 1968 International Cup for Formula One Manufacturers.  The 80-lap race was won by Jo Siffert, his first Formula One victory, and the first victory by a Swiss driver.

1996 Monaco Grand Prix: The 1996 Monaco Grand Prix (formally the LIV Grand Prix Automobile de Monaco) was a Formula One motor race held at Monaco on 19 May 1996.  It was the sixth race of the 1996 Formula One season.  The race was run in wet weather, causing significant attrition and setting a record for the fewest number of cars (3) to be running at the end of a Grand Prix race.  Olivier Panis scored his sole career Formula One victory, earning the last ever Formula One victory for the Ligier team (and the first ever for engine manufacturer Mugen Motorsports) after switching to slick tyres in a well-timed pitstop.  s of 2017 , this is the most recent race won by a French driver.  Johnny Herbert scored his only point of the season.

1962 French Grand Prix: The 1962 French Grand Prix was a Formula One motor race held at Rouen-Les-Essarts on 8 July 1962.  It was race 4 of 9 in both the 1962 World Championship of Drivers and the 1962 International Cup for Formula One Manufacturers.  The race was won by Dan Gurney, his first Formula One victory, driving a Porsche, that company's only win as a constructor in a Formula One championship race coming after three years of racing.  It was the third time that the French Grand Prix was held at Rouen, last time being 1957.

Eagle Mk1: The Eagle Mk1, commonly referred to as the Eagle T1G, was a Formula One racing car, designed by Len Terry for Dan Gurney's Anglo American Racers team.  The Eagle, introduced for the start of the 1966 Formula One season, is often regarded as being one of the most beautiful Grand Prix cars ever raced at the top levels of international motorsport.  Initially appearing with a 2.7L Coventry Climax inline 4-cylinder engine, the car was designed around a 3.0L Gurney-Weslake V12 which was introduced after its first four races.  In the hands of team boss Gurney, the Eagle-Weslake won the 1967 Belgian Grand Prix, making Dan Gurney only the second driver at the time, and one of only three to date, to win a Formula One Grand Prix in a car of their own construction.  That win in Belgium still stands as the only Formula One victory for a United States-built car.

Jo Siffert: Joseph Siffert (7 July 1936 – 24 October 1971) was a Swiss racing driver.

Supporting paragraphs: 1968 British Grand Prix Jo Siffert
Answer: 7 July 1936