We don't have a specific date of birth for Baldor, but we do know that he was the eldest of King Brego's sons. Given that his younger brother Aldor was known to have been born in III 2544, it follows that Baldor must have been born before that date.

Different sources imply different dates for the loss of Baldor. The Tale of Years is explicit that he vanished into the Paths of the Dead in III 2570, but that date is in slight disagreement with the description of the Kings of the Mark in Appendix A to The Lord of the Rings. There, it's said that Baldor's father Brego died of grief 'the next year' after Baldor's loss, but it's also said that Brego died in III 2570, which would date the loss of Baldor as III 2569.

It's hard to fully account for this discrepancy, but it seems to have arisen because of a change in the chronology. In its original form, the Tale of Years had the Golden Hall completed in III 2569 (a fact that is constant across all versions) but then Baldor vowed to pass the Forbidden Door a year later in III 2570. This story was later adjusted, so that Baldor made his vow at the first feast in the new hall (that is, a year earlier than in the older version). The account of Baldor's end in the Tale of Years should presumably then have been moved back from III 2570 to III 2569, but instead it remained under the old date, throwing the chronology out by a year.

So, though it's impossible to be absolutely sure how these dates should fit together, the most likely dating would seem to be that Baldor was actually lost in III 2569 (contrary to the Tale of Years), and his father died of grief the following year, III 2570.