I've been trying to piece together Xylo's timeline based on the information we currently have. **This is just my personal theory, so feel free to correct me if I missed anything! :)** 

We know that Penal Hero Unit 9004 was founded at most **20 years before the present**, while **Dotta joined 4 years ago,** leaving a **16-year window.** Since Xylo joined **after** Rhyno (Puck Puca), Tatsuya, Venetim, **but before** Dotta, his sentencing must have happened somewhere within those 16 years.

With information that the Og!Rhyno admired Holy Knight Xylo, meaning Og!Rhyno encountered Puck Puca **after** Xylo had already become a renowned Holy Knight, but **before** Penal Hero Unit 9004 was established.That suggests Xylo was already a well-established holy knight at the time, likely in his early twenties.

Another clue is that Xylo was sentenced **before he can marrying his fiancée**. Since she came from a noble family, I think it's reasonable to assume they were expected to marry relatively young, as arranged noble marriages typically happened in their twenties.

So with that Noble marriage things, I think **around 30 years** **old would be the latest** **Xylo could have been sentenced**, with his late twenties being the more likely range. It seems unlikely that his fiancée's family would have delayed the marriage much longer than that.

Based on those assumptions, if Xylo became a Holy Knight at **around 20 years old** and was **sentenced between 25–30,** then he likely joined Penal Hero Unit 9004 roughly **5–10 years after its formation**. That would mean he's probably **served in the Penal Hero Unit for around 10–15 years**, with **16** **years being the maximum** if he joined shortly after the unit was founded.

*Note: If we allow Xylo to have been sentenced as late as 35 instead of 30, then his estimated time in Penal Hero Unit 9004 widens to 5–15 years instead of 10–15 years.*

Estimating Xylo's Age When He Was Sentenced and Years Served