Probably he is the Gerald Aubrey H Hallifax who is born in the BMD index for Dec qtr of 1874 in Kingsbridge dist, vol 5b, p. 201.
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His baptism:

First name(s)           Gerald Aubrey Hays
Last name               Hallifax
Birth year              1874
Birth date              17 Oct 1874
Baptism year            1874
Baptism date            19 Dec 1874
Denomination            Anglican
Baptism place           Stokenham
Father's first name(s)  Albert Rard  [sic, but the original register has ‘Albert Praed’ ]
Mother's first name(s)  Isabella Aubrey
County                  Devon
Archive                 South West Heritage Trust
Archive reference       3031A/PR/1/5
Record set              Devon Baptisms

The Baptism register image adds:

Abode:         Halwell in the parish of South Pool
Father’s job:  Gentleman
Celebrant:     W D Pitman, Rector of Aveton Gifford
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He was joint MFH for the Tetcott Hounds of Devon.  A report of the 1906 Opening meet, with 200 present, can be found in the Western Times of 9th November 1906, p.9.

In 1908 on retiring from MFH he was presented with a clock.
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In 1911, he had this household where his parents had lived:

Name Relation Condition/ Yrs married Sex Age Birth Year  Occupation  Where Born

HALLIFAX, Gerald Aubry Hays  Head         Single  M  36  1875  Independent Means  S Devon South Pool
PHILLIPS, Rebecca            Housekeeper  Single  F  52  1859  Housekeeper        S Devon South Pool
PHILLIPS, Dora Violet        Boarder      Single  F  22  1889  School Teacher     S Devon South Pool

RG number: RG14 Piece: 12869 Reference: RG14PN12869 RG78PN743A RD274 SD2 ED7 SN51

Registration District: Kingsbridge Sub District: Stokenham EnumerationDistrict: 7
Parish: South Pool

Address: Halwell House South Pool Kingsbridge
County: Devonshire
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No death record on FindMyPast.  But FreeBMD has:

Surname   First name(s)  Age  District  Vol  Page
Deaths Jun 1912   (>99%)
HALLIFAX  Gerald A H     37   Totnes    5b   228

and on the new GRO index:

Name                             Age at Death (in years):  
HALLIFAX, GERALD  AUBREY HAYES   37  
GRO Reference: 1912  J Quarter in TOTNES  Volume 05B  Page 228

And the inquest has been transcribed from the Western Times of 29th April 1912:

Western Times, Monday 29 April 1912
UGBOROUGH - The Fatality At Dartmoor Hunt Races.  "Going The Pace."  -  The tragic death of MR GERALD AUBERY HAYES HALLIFAX, of Halwill House, South Pool, near Kingsbridge, has caused a feeling of grief throughout South Devon, the deceased being a popular and beloved gentleman, especially in sporting circles.  He was only 37 years of age.   -   Mr P. C. Cornish Bowden, Deputy Coroner, held an Inquest at Langford farm-house in the parish of Ugborough, on Saturday morning.  Mr W. H. Heath was chosen Foreman, and Supt. Jeffery watched the case on behalf of the Police.  - Mr Charles H. Calmady Hamlyn, J.P., of Bridestowe, gave evidence of identification, and said that MR HALLIFAX had been suffering from influenza, but had practically recovered and in his opinion was in a fit condition to ride in the race.  He saw him just previous to the start, and watched him in the race which he desired to win.  It was true he was "going the pace."  He was a fine horseman and had hunted the hounds regularly.  At one time he acted as joint master of the Tetcott Fox Hounds.  The course was fair hunting ground.  Witness saw him descend one part at great speed and clear the bank.  The ground there had an ascent and from what witness could gather the horse plunged the bank, pitched its rider over and then fell on him.  Witness hastened to the spot only to find him dead.  -  Captain Charles F. Burnard was next called and said he was riding in the dame race and he and deceased wee near rivals.  Witness, however, had fallen at the previous bank, but re-mounted and chased deceased about five hundred yards behind.  They were both riding at fast speed - really faster than was safe to take a bank.  Witness saw MR HALLIFAX fall and succeeded in pulling his own horse to the right side and avoided jumping over the bank on him.  The banks were quite safe and in good order.  The ground was very hard but in no way dangerous for riding.  -   Mr Alfred A. Partridge of Plumpton, said he was the owner of the horse, which was known as "Pedlar."  It was 8 years old and had hunted with the Dartmoor Hounds for three years, was a good banker and never had a previous accident.  MR HALLIFAX had ridden it before and knew it very well.  -  The Coroner:  Can you account for its falling?  -  Mr Partridge:  Only that the speed was exceedingly fast.  -  Dr W. T. Webb of Kingsbridge, deposed to watching MR HALLIFAX during the race.  He saw the horse fall and ran to the spot, but found him quite dead from a broken neck.   -   Mr Haldene, of Plymouth, and Mr Ham, of Ugborough, also gave evidence.   -   The Jury returned a verdict of "Accidental Death," and passed a vote of condolence with the deceased's family.
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His probate index:

HALLIFAX< Gerald Aubrey Hays of Halwell House South Pool Kingsbridge Devonshire esquire died 26 April 1912 at Wrangaton Devonshire  Administration Exeter 11 June to Ethel Aubrey Proude (wife of Ashley Anthony Proude) Effects £18280 8s. 1d.
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