I just saw your posted message. Is he straining to urinate or defecate?
I will be online for another hour, and will wait for your reply.
I am not sure how your cat is doing now. If he is still meowing and straining, I recommend you take him to a veterinarian ASAP. Male cats of any age can develop a bladder obstruction due to inflammation, stones or crystals. This is a medical issue that needs immediate attention.
If he is straining to defecate and vomiting, he has an intestinal problem. He may need to be rehydrated and given medication to settle is stomach.
The veterinarian can also do some screening bloodwork to make sure he does not have kidney, liver, or thyroid disease that could affect him.
Please let me know if you have other questions. I am here to help. I would appreciate any updates with how he is doing.