Είχα να πάω σε βάφτιση από τότε που ήταν μικρή η ξαδέρφη μου.

This is a very common Greek pattern: έχω / είχα να + verb.

It is used to say that a long time has passed since someone last did something, or that they had not done something for some time up to a point in the past.

So here, είχα να πάω σε βάφτιση... means something like:

• I hadn’t been to a christening...
• It had been a long time since I had gone to a christening...

Even though είχα by itself just means I had, in this structure it creates that it had been since... / I hadn’t done... for a long time meaning.

Because έχω / είχα να is a fixed grammatical construction in Greek.

After να, Greek normally uses the form that learners often call the subjunctive form. So:

• να πάω
• να δω
• να φύγω

In this sentence, να does not mean in order to. It is just part of the structure είχα να πάω, which expresses how long it had been since I went.

After να, Greek uses a specific verb form.

Here πάω is the aorist subjunctive form of πηγαίνω / πάω. In this structure, Greek usually uses the aorist form because it refers to the action as a whole: to go / to have gone.

So:

• να πάω = to go / to have gone
• not πήγα, because πήγα is a past tense form and does not come after να
• not usually να πηγαίνω, because that would suggest repeated or ongoing going, which is not the idea here

So είχα να πάω means I hadn’t gone / it had been a long time since I went, not I hadn’t been going.

Greek often leaves out the article after σε when talking about going to a type of event, place, or activity in a general, non-specific way.

So σε βάφτιση means:

• to a christening
• to a baptism

This is very natural Greek.

You could also hear:

• σε μια βάφτιση = to a christening, with a bit more emphasis on one / a certain christening

But in this sentence, σε βάφτιση sounds more natural and general.

Από τότε που is a very common way to say since when it introduces a whole clause.

So:

• από τότε που ήταν μικρή η ξαδέρφη μου
  = since my cousin was little

Literally, it is something like:

• from the time that...

Greek often uses:

• από τότε που... = since...
• τότε που... = when... in the sense of back when...

In this sentence, it marks the starting point in the past.

Because ήταν describes a past state, not a single completed action.

ήταν μικρή means:

• she was little
• she was young

That is a description of what she was like at that time, so Greek uses the imperfect:

• ήταν = was

This is very normal when talking about age, size, condition, or background in the past.

Because μικρή agrees with η ξαδέρφη μου, which is:

• feminine
• singular

Greek adjectives must agree with the noun they describe.

So:

• μικρός = masculine singular
• μικρή = feminine singular
• μικρό = neuter singular

Since ξαδέρφη is feminine, the adjective must also be feminine: μικρή.

Literally, μικρή can mean small or little, but in this context it is understood as young / little in age.

So όταν ήταν μικρή is a very common way to say:

• when she was little
• when she was young

Greek uses μικρός / μικρή / μικρό this way very often about children.

Both are possible.

Greek word order is more flexible than English. The version in your sentence puts the subject η ξαδέρφη μου after the verb and adjective:

• ήταν μικρή η ξαδέρφη μου

This sounds natural and often gives a slightly more flowing, conversational feel.

The more straightforward order would be:

• η ξαδέρφη μου ήταν μικρή

There is no major difference in basic meaning. Greek often moves the subject later in the sentence, especially when the subject is already known or not the main focus.

Because Greek possessive words like μου, σου, του, της usually come after the noun.

So:

• η ξαδέρφη μου = my cousin
• το βιβλίο μου = my book
• ο φίλος της = her friend

This is the normal Greek pattern. English puts my before the noun, but Greek uses this short possessive form after it.

Yes, and that would also be correct Greek, but it is a slightly different structure.

Compare:

• Είχα να πάω σε βάφτιση από τότε που...
• Δεν είχα πάει σε βάφτιση από τότε που...

The second version is more directly I had not gone to a christening since...

The actual sentence uses the idiomatic pattern είχα να πάω, which emphasizes the idea that a long stretch of time had passed since the last time.

So both can work, but είχα να πάω is a very natural Greek way to express this idea.