One of my players is shortly becoming a Saint but I took a different approach.
He will take the template at 18th level (he's 17th and short of a Feat and he has been nothing but a Saint since day one...). I told him that when he reached 18th level he would be just an 18th level Cleric, and for the next two levels he would have to gain the experience without using it to "advance" in class levels.
When he gets enough XP to be 20th level he would gain the saint template and be considered a "20th" level character.
He will take the template at 18th level (he's 17th and short of a Feat and he has been nothing but a Saint since day one...). I told him that when he reached 18th level he would be just an 18th level Cleric, and for the next two levels he would have to gain the experience without using it to "advance" in class levels.
When he gets enough XP to be 20th level he would gain the saint template and be considered a "20th" level character.