Just wanted to bring this up:
Where does it say LOI took place in 1094? I haven't read all of the documentation and references, but the Konami website says the Castlevania saga started in 1094; it doesn't say LoI took place in 1094. The Japanese Wiki doesn't even say it took place in 1094, just the English Wiki. So if all anyone is going off of is the Konami timeline, then technically there's nothing wrong with the date at all -- it would be Leon's birthyear.
The First Crusades started in 1095 when the Byzantine empire asked for aid to defend against the Turks. The Crusades lasted many, many years. The Venetian Crusade was in 1122, which would have put Leon at the age of 27 or 28. The Damascus Crusade was 1129, which was when the Templars were officially recognized by the papacy. Thus by the time of the Templars, if Leon was born in 1094 rather than the game taking place in 1094, Leon should have been in his early 30s.
So it wouldn't be a mistake on Konami's part, but a misinterpretation of the chronology.