Thank you for your question regarding your boy Wilson who you want to give Aspirin to. In short - the answer is definitely no, please do not give Wilson any Apsirin at all. Because of the way in which cats metabolize this drug, it is actually very toxic to them. You can read more about aspirin toxicity in cats online here: http://www.petmd.com/cat/conditions/digestive/c_ct_aspirin_tox . Unfortunately, pretty much all human anti inflammatory drugs are toxic to cats, so please don't be tempted to give any other pain medications such as Tylenol or Advil - all of these are toxic to cats and will likely cause much more harm than good.
The best way forward here is to get a licensed veterinary anti inflammatory for Wilson and I would recommend metacam for him. You can read more about metacam online here: https://www.metacam.com/ . You will need to get this from your local vet after they carry out a full physical exam on your boy however.
Because it is evening now, you are best to keep an eye on your boy. It will be cheaper to go to your regular vet tomorrow rather than an ER vet now, however if Wilson is in pain, then you do need to get him seen now. For now, please keep an eye your boy's mucus membranes, capillary refill time and respiratory rate tonight as follows (do be careful that your boy doesn't try to bite you):
Mucus membranes - flip his lip and look at the color of his gums. They should maintain a nice salmon pink color. Get him to the emergency Vet if they appear white or very pale pink, or if they are a dark deep red color.
Capillary Refill time - this measures blood perfusion and test this by putting your thumb on his gum to apply pressure. After you release your thumb you will see the gum blanch. Capillary refill time is the amount of time it takes (in seconds) for the gum to return to a healthy pink color from the blanched white color. If 2 seconds or less don't worry - if it is taking significantly more time, again - off to the emergency Vet.
Respiratory Rate - if he is continuously panting or open mouth breathing at all tonight, this is a sign of shock and or pain and a signal for a trip to the emergency Vet.
I hope all of the above makes sense? If you have more questions or if I can help in any other way, please do not hesitate to ask! If you would like to accept my answer, please press RATE OUR CONVERSATION (I am not compensated in any other way). Bonuses are always welcome. Thanks! I hope to work with you again soon!
PS: If you have additional questions after you rate the question, you are welcome to request me for additional conversations if I am on-line or by beginning your question "Dr. E..." or "Pet-doc..." and others will leave the questions for me.