Soldiers' records?

[Abhanliath]

I have someone here who died of General Parlysis of the Insane, poor man. Which is to say syphilis, a disease that's been virtually wiped out in the West by antibiotics.
I'm wondering if he might have been a soldier. How would I find this out? Are there any openly available lists of Irish soldiers serving in the British (I assume, but I suppose could be US) army up to, say, 1890?

[Andy J2022]

Bear in mind that between 1800 and 1922,  Ireland was part of Britain, politically speaking, and so any Irishman who wanted to join the Army, de facto, joined the British Army. The extent to which military records for the nineteenth century survive is variable, but those that do exist can mostly be found on Ancestry or FindMyPast. The main sources which haven't yet been digitized (and won't be for some time) are the muster rolls of the various regiments. Obviously if the person you are interested in had a common name you will have a better chance of finding him if you have plenty of other information such as his date and place of birth and a rough date for when he might have joined up.
The way you have phrased your question makes me think that you believe that being in the Army was the most likely reason for him catching syphilis, possibly due to serving overseas. Syphilis was still fairly widespread in the British Isles at the end of the nineteenth century so he is just as likely to have contracted it as a civilian at home. Antibiotics weren't used until after WW2, fifty years later.

[Milliepede]

What year was this/how old was he - do you have any other records on him that give an occupation?

[Abhanliath]

He was born in or near 1854. The only occupation I know him to have is gardener; however, I'm wondering if he might have spent some time soldiering, purely because there are fewer chances of contracting the syph among the roses. In Ireland at that time soldiers were the main carriers of venereal disease, or so I read.

[Milliepede]

How old was he when he died?  Was he married or single?

[Abhanliath]

Yes, Andy, the British Army is the most likely, though someone born in 1850 could certainly have gone to America at 16 in time for the American Civil War, especially as 1850 was the fifth year of the Great Famine when people were flooding out of the country. I'm not saying he did, just that it's a possiblility.

[Abhanliath]

He married and fathered four children in that marriage before dying.

[Milliepede]

Need to know what year/age he died. 

Were all the children born in the same place?  to indicate he wasn't moving around soldiering.

[Abhanliath]

His soldiering would have been in the past, if it existed at all. This is probably a false road - it just struck me to take a look if the records were open and freely available; if they're not, I'll leave him behind.
Thanks for all the help!