Domicile is decided by complicated rules, which are quite different from ‘residence’. Residence is where you currently live. Domicile is your ‘homeland’. Different countries have different rules, but basically if you live more than 6 months in Ireland (or England), you are likely to become a tax resident in that country and have to pay taxes on income arising there. If you are also domiciled in that country, you also have to pay tax on your foreign income as well. However if you are domiciled elsewhere, you only pay tax on foreign income if you ‘remit’ this to the country you live in. Otherwise it is only liable to foreign tax (if any). You can of course remit capital without penalty at any time.
At birth you get your father’s domicile. It would certainly change if you emigrate before 16 years of age and live permanently in your new country. It would change if you move abroad, settle, and marry a native UNLESS either (1) you maintain a Will made under the law of your original domicile (say England) AND make some indication that you may die in England AND retain some connections with England (eg bank account); OR (2) you move to a third country / keep travelling.
In all other circumstances it is difficult but not impossible to acquire a new domicile. Basically, you are stuck with England unless you make a new life in another country, continue to live there as your sole residence, cut all your economic ties with England, AND ESPECIALLY make a Will under the law of your new domicile including a statement that you wished to be buried there.
People who simply retire abroad are very unlikely to change their domicile unless they have ancestral connections with the country they retire to.