Welcome to Microsoft Community, and thank you for reaching out!
I understand that in this present generation, our emails are very valuable to us, and it's also important to keep track of all of the emails, even the old ones.
The Outlook app for Android is only capable of handling one month's worth of messages. You can only receive emails not older than 30 days, and it's because of the
mail days to sync option that can be configured up to 30 days only. You can search for older emails, once you reach the bottom of the page, just tap
Load More (this option may vary).
A settings extending the sync duration would be a great recommendation and thank you for bringing this to our attention. Microsoft continuously strives to improve its products
and to provide a better experience to its consumers. At this point, we would like to have our engineers be aware of the said concern. I would recommend posting your concern
on our Outlook UserVoice. Through this, our support engineers will be able to collate data and supporting details regarding this
and might consider adding the feature as a good ground for future updates.
Should you need further assistance, feel free to post back to Microsoft Community.