Cat behaviour: fighting or playing

Question
Last April I adopted an elderly cat because his owner could not take him with her.  He is nearly 14.  My partner has recently had to move house and is unable to take his cat with him.  His cat is also a male, but only 4.  His cat, Charlie, has moved in with me and my cat.  Although me and my partner are not living together, he spends  lot of time at mine, so still gets to see Charlie a lot.  Charlie moved in 2 weeks ago and I kept him in for the first week to get him used to his new surroundings.  He seems happy feeding and using the litter tray.  He now comes and goes as he pleases, along with my cat, using the cat-flap.  The two cats seem to get on most of the time, they will often both be sleeping on the end of my bed.  However, there are times in the day where they appear to fight.  It is difficult to tell whether it is nasty fighting or play-fighting.  And it can be started by one or the other of them.  Charlie may pounce on my cat, or vise versa.  Lots of fur (mainly from Cahrlie!) tends to fly but there appear to be no injuries.  I am concerned that my cat is not being put under any pressure with this much younger cat being around, but on the other hand, it may be giving him a new lease of life!  How do i tell whether they are playing or whether they are just not getting along?  Are there any other indicators that i should look for to tell me whether they will be able to live happily together?  Thanks and i look forward to hearing from you.  Jill.

Answer
Jill,

Your cat is 72 years old in human years. Charlie is 32 in human years. More than likely Charlie wants to play and your cat doesn't and gets cranky. Other times your cat may feel frisky. If they are sleeping together and getting along otherwise then I wouldn't worry to much. What looks rough to us is not to cats.

Warning signs are pinned back ears and blood being shed, plus lots of fur flying. Hissing and growling is just kitty comunication.

Just keep an eye on them and if your cats looks stressed or tired call a time out or give them both a treat to distract them.

Getting a pet laser light (PetSmart, Petco, etc.) is a good way for both cats to play interactively. They focus on chasing the 'little red bug' and not each other.

Just for reference and future information here is a good site with articles about the elderly cat that you may find helpful:
(copy and paste, or type the whole link into your address bar)

http://www.sniksnak.com/resources/geriatric.html

I hope this helped

Carol