My 14 years old cat seems to have problems with defecating. It happens less often than before and usually he was super duper happy after he's done (don't know why, he got this habit from kittenhood, to run about the flat when he has done the thing). Now he isn't like that, he doesn't seem to get much relief from it and the process itself doens't go easy. Is it safe to give him an enema? What else I could give him to make the process easier?
Cats can have constipation because of different reasons such as excessive hair loss (for example in shedding periods) and hair balls as a result, too much dry food, worms, tumors, etc. Older cats tend to suffer from constipation more often because their intestinal function gets weaker and they are more prone to dehydration.

How long has your kitty had this problem? If it's the first time he's having it, I'd not give him an enema right away. Try something else like re-considering his diet in favour of softer food and brushing him more frequently. Also, you could give him some vaseline or castor oil (1-1,5 ml per 1 kg of his weight). When our Barsik had probs with pooing, we tried to add some beetroot pieces to his daily diet and it helped.

If this doesn't help and he keeps on having constipation every now and then, or if you notice serious behaviour changes, taking him to a vet would be a good idea like kittehlewis said.
i wouldnt sugest doing an enima yourself it might sound a simple process but things can always go wrong so best to get your vet to do that is they think neccisary other then that what food are you feeding him? prehaps a change of diet will help something a little more digestable for the older cat
 Ruslana's reply was promoted to an answer.
Cats may not poo for 3-4 days if they've had a stress, it's absolutely normal. Provided that there are no signs of discomfort and efforts to defecate of course. Have there recently been anything that could cause stress to your cat?