Thanks for the article. She doesn't seem to have any visible or noticeble physical or cognitive impairment. On her last Vet visit they didn't do any bloodwork, which kind of disappointed me considering her age and the fact that she hasn't had a blood test for a very long time. She doesn't exactly 'yowl' at night, it's just a regular meow like she does during the day. She has yowled at times, but very rarely, and every time I put her in the carrier to take her to the Vet. She yowls and screams the whole time. She seems to be getting very clingy and wants to be petted often. But like cats do, once she has been petted enough, she will quiet down and either play or lay down for a nap. But she's either napping or bouncing off the walls, usually nothing in between. Very hyper for a 16 yr old. Last time I had her at the Vet they had a chart on the wall for dogs and cats age compared to human years. According to the chart a 16 yr old cat is equal to an 80 yr old human. I hope I'm as playful when (and if) I am 80!