As already mentioned there is no pronoun in the Welsh above so it's referring to 'retiring' as a general activity rather than 'my retirement'.
To refer to a person the pronoun is necessary here:-
After I retired = Ar ôl i fi(SW)/mi(NW) ymddeol (SW = South Wales, NW = North Wales)
After you(familiar) retired = Ar ôl i ti ymddeol
After we retired = Ar ôl i ni ymddeol
In the usual colloquial language, the subject pronoun used in association with a verb is i - this is the main one to remember. It is also used with some prepositions. For example:
- dw i - I am
- bydda i - I will be
- es i - I went
- gwnes i - I did/made
- arna i - on me
- *amdana i - about me
- gen i - by me (or indicating possession)
As a standalone pronoun, or when used with some other prepositions, it is usually fi. fi is also often used with some other prepositions. For example:
- fi - me (as a standalone pronoun)
- gyda fi - (together) with me (or indicating possession in some dialects)
- efo fi - (together) with me (in some dialects)
- fi biau... - I own... (biau is a very irregular verb)
- i fi (or i mi) - to me
However, you will sometimes find fi used in place of i in some situations or in some dialects. There can be quite a wide overlap.
Things are different in the more formal registers of Welsh, and also in some very casual use of the language, but this course does not cover either of those.
[The word mi also has another use in some dialects, not as a pronoun, that you will meet in other parts of the course]