The last post on her Instagram is her speaking to a 74 year old lady, the interview seems to be focusing on age, and she says she "surrounds myself with young people, over and over again, always". Maybe that's Naomi's plan too. Have a baby around to keep her young. Maybe I'm projecting but seems to be an odd idea that if you look young, you're somehow younger than your actual age. You're not.
My parents were older (middle - late 40s), and I had a happy childhood, but it's not ideal, especially as you both get older. From my own selfish point of view, I wish that they had been younger. I was jealous of friends with parents in their 20s and 30s when I was younger, as mine didn't want to do kids things (I'm the youngest of 3 and so age might not have had anything to do with that). And now I am sorely jealous of friends whose parents are in their 50s and 60s, active, babysit for them regularly, while I am worrying that mine won't be able to cope at home much longer.
So yep, I would say in Naomi Campbell's case it does seem a bit selfish to have a baby at 50. Why not just do it sooner, it's not like money is an issue, she could have afforded "the science" 
before. Though I'm sure that there are plenty of men who become dads over 50 and no one bats an eye lid, but I suppose that their partner is at least 10 years younger. At least she has enough cash that her child won't be worrying about nursing home fees in 25 + years.