Thank you both for your replies.
I have figured out from later census records he was born in 1860, or very close to 1860. Here is the additional info on him:
Born Bushmills, County Antrim, Ireland, and having worked as a labourer, then attested for service with the British Army at Londonderry on 30th July 1879, joining as a Gunner (No.7972) the Royal Artillery, for service with the 3rd Division. He then transferred into the Royal Horse Artillery on 1st October 1879, and with the reformation of the army, then saw service with ‘B’ Battery from July 1881, being appointed to paid Acing Bombardier on 26th August 1881, before transferred as a Gunner to A/A Battery on 1st April 1882, and then transferred as a Driver / Gunner to the Riding Detachment on 1st August 1883. Appointed to Acting Bombardier in July 1884, and then promoted to Bombardier on 22nd August 1884, he was then tried and reduced to the ranks on 10th July 1885, but had his sentence immediately squashed and he continued as before. Fullerton was posted to the 2nd Cavalry Brigade as a Bombardier from 1st October 1885, and was once again tried and reduced and this time his sentence was upheld on 24th May 1886. He then transferred as a Gunner to “A” Battery RHA on 22nd August 1886, and was appointed to Acting Bombardier again on 31st March 1887, before being promoted to Bombardier again on 22nd January 1889, and then promoted to Corporal on 23rd May 1889. Owing to a re-organisation he then found himself serving with ’N’ Battery from 1st July 1889 before being posted out to India from 1st October 1889. He was out there where he was again tried and convicted, and this time reduced to Bombardier on 18th March 1893, before being transferred to ‘Q’ Battery on 1st December 1894, and posted home on 5th November 1895. Promoted to Corporal again on 7th February 1896, he was once again tried and reduced to Bombardier on 28th July 1896. Owing to the outbreak of the Boer War he was then posted to South Africa from 19th December 1899, and was then present with ‘Q’ Battery in action at the relief of Kimberley on 15th February 1900, at Paardeberg between 17th and 26th February 1900, and at Driefontein on 10th March 1900. Fullerton was then severely wounded in action at Sanna's Post on 31st March 1900. Source: WO97. Mkt
Thank you