They use one term and stick to it. Don't worry about terminology. Use lactose intolerance. Everybody will know what you mean. I'm lactose intolerant, but neither of my parents are.
Some people produce lactase all of their lives.
Others find that their lactase production gradually slows or even stops as they grow older. This is controlled by a gene on the second of the 46 pairs of chromosomes that humans have. One set of each pair of genes comes from our fathers and one set from our mothers. The go gene is dominant and the stop gene is recessive. That means that if you have a stop and a go, go always wins.