I'm of the opinion that unless they are coming to Xmas or we see them a lot then when the extended family (nephews nieces, god children) turn 18 or start working then that's a good cut off point for Xmas presents.
Also when do the younger members start buying presents for the rest of the family? My DN 25 earns £40+ and doesn't buy any presents even for his younger cousins. I wouldn't say anything he's a lovely person but I think there comes a time when he has to join in.
What are your thoughts