Lol! When I turned 16, my aunts/uncles/grandparents/parents all chipped in for a "hope chest". Every birthday and Christmas after that, I received gifts to put in the hope chest (sheets, towels, small appliances, etc)...and Christmas 18 was the magical cut off when no more gifts were given by aunts and uncles. This was the same way for siblings, starting with my older sister, so we all knew going into our 16th Christmas what our presents would be like for the next two years. That having been said ... the best birthday gift I got was a linen doily, embroidered with silk threads which had been given to my grandmother and grandfather as a wedding gift in 1919. I have it framed now and up on the wall in my bedroom.
Due to family issues -- my family has never bought presents for my DKS, and I don't remember the last time that I bought a gift for one of my siblings' children. I did take sister, niece and three grandnieces out to a nice dinner and had a girl night with them when I was back in the midwest in October, but that is a once every 3 years event.
DH's family agreed years ago that we would buy gifts for only the kids, and once you hit 21 -- you weren't a kid anymore. So this year we buy for six, but next year we buy for five, and the year after we buy for four. YDS aged out this year, he turned 21.