Cupid, this sounds very much like Rover's symptoms - see if you can phone the vet now and get a blood test for your cat a.s.a.p. after Christmas. Rover was throwing up every time he ate - it was due to bile caused by kidney problems (which are very common in older cats). He was put on tablets and was as right as rain in no time.
Furballs are very obvious, you get a dollop or tube of fur surrounded by liquid.
If it's undigested food, get him looked at - if it's the same as Rover's, it can be kept at bay.
He should be on senior cat food at his age, and good quality stuff - it contains the vitamins and minerals an older cat needs.
Good luck to you both!