To say what you are, i.e. what profession you have, we say 'Dw i'n ...'

The pattern for 'I'm retired' is a little different; we say:

Dw i wedi ymddeol

Sometimes we use a mixed sentence, where the object comes before the verb. This applies emphasis to the sentence, er enghraifft (for example) :

Athro dw i

This sentence emphasises the fact that you're a teacher.

You can't use this pattern for talking about places of work, or for saying that you're retired.