Why does my cat cry?

My cat yowls all the time. Why? He is 15 years old, a tabby, and a very fussy eater. Does he do this for attention? He particularly does it at night but does it in the day time too. Is something wrong next to him? PLZ I need help!!
Loneliness?
My cat does it too. Since my boyfriend and I broke up, Lexi yowls all hours of darkness. I am not sure if it is because she misses him, or misses him playing hard beside her. I go to bed and she makes her presence known from the kitchen. It drives me nuts. But her appetite is biddable, her energy level is good. Last Friday dark there was a serious car happenstance on one of the city streets and it knocked out power for several blocks. She yowled for two hours. Until I got out of bed, and she looked me right in my eyes and started knock over candlesticks, books, and pictures off of the shelves. She was mad because the warmth was off and it was 22 degree outside. Cats have cattitude, and if they are ingestion well and have good perkiness, then chances are they are fine. If his eyes are clear and bright and doesn't have the eyelid closing partially way, then he is fine. Just getting set in his ways. Rub his stomach for me!
Answers:    At his age he needs a senior checkup at the vet. As cats return with older they can suffer from dementia, internal organ problems, or diseases. He could just want attention but I'd really have him looked at basically to set your mind at ease.
my boyfriends kitten yowls ALL the time, too. but hes only similar to 4 months old.
why does your 15 year old cat yowl,,because he/she is hurting .. see a vet honest
My babe kittens are dying?   My two 3-year antiquated cats are other meowing for food. Why?   It is NOT not dangerous for me to put a drink down near my cat?   What can i offer my cat for misery ?