So you plan to sear the 23 week old cockerel then simmering for 30 minutes. I do not cook them that way. Be careful on the frying, frying is a good way to turn the cockerel really tough. Not sure how simmering for a half hour will work out, either tenderness or fully cooking it. If you cook it faster than a slow simmer you may have texture problems.
Not sure where you are located so I don't know about the chicken you buy at your store. In the US, the chicken in the store is around 6 to 8 weeks old. It is really tender and can be cooked any way, including frying or grilling. A 23 week old cockerel would not handle frying or grilling well. You can certainly try your method, sounds delicious, but don't be surprised at a difference in texture.
The main reason I asked about the recipe was for suggestions on how to handle it after you butcher it.
You will need to age your chicken before you start. A few hours after death rigor mortis will set up. If you cook it immediately after butchering this is not an issue, but when rigor mortis sets up the chicken will be extremely tough. So you need to age it until rigor has passed. That's usually about two full days (48 hours) but some can take a little longer. If you are not cutting it into serving pieces before you cook or freeze it, rigor has passed when you can easily wiggle a thigh or wing. It's really floppy. If you cut it into serving pieces those need to be loose, not stiff at all. Age it in the fridge or in a cooler filled with ice water.
Some people brine their meat while it is aging. That means they add salt to the mix as it ages. I don't think need to do that. You can add salt later for the salt flavor. Brining causes the meat to retain moisture. That's really handy when you are cooking it with a dry method like frying, grilling, or roasting. If you cook it with a moist method it's not necessary. With your hybrid frying/simmering I don't think it would be necessary but it won't hurt. To me purely optional.
Now the fun part, marinade. You can add all kinds of flavors with marinade, but you can add those flavors without marinading. A marinade is generally made with an acid, vinegar or wine being two really popular ones. The acid breaks down fibers, tenderizing the bird. The strength of the acid and how long it is left in will have a big effect on how much it tenderizes it. If you just use dry herbs when you are keeping it in the fridge overnight it probably won't have much, if any, tenderizing effect. Italian seasoning probably has vinegar in it, you could get an effect. Then you are cooking it in wine. That wine will have some tenderizing effect.
I don't know how your recipe will turn out texture-wise with a 23 week old cockerel, I think it has a chance. There is only one way to find out. Good luck and let us know how it turns out.