You can look into "decrowed" roos (could be cost prohibitive and it's a debatable topic), try some of the "fixes" (ie a crow collar - questionable effectiveness) or, probably easiest and most effective - purchase fertilized eggs for hatching.
Babies are so cheap with cornish rock it's really not worth the trouble to try a sustainable flock imho. It is extremely hard to get them up to egg laying age without their carriage giving out under their weight, or for them to just keel over from respiratory problems. It doesn't help with the crowing but slow broilers would be a better option for sustainability.
The oldest one I ever hear of was a friend had a rooster live 3 years. He was 24 lbs after he died. I don't believe he had any hens live long enough to give eggs though. I imagine if someone really restricted their feed they may have a regimen to get them to adulthood with expected loses along the way. I wouldn't want to invest the time and money myself though.
I have 4 CX pullets giving me eggs 2.5 eggs/day. They didn't hit freezer camp last year and wintered just fine. They were saved for this purpose to breed back a crossbred g2. I did have a rooster my 1st year with meats WAY past the 8 weeks and he did crow loudly. And whenever he walked he shook the ground with a thump. I was looking for beef cattle sneaking up on me. But was him in the barn. mainly they free range with my layer flock (DP breeds) and rouen duck pair. They only get table scraps, some shelled corn and whatever they get on range. No health issues leg/heart attack etc. This week we have 60 CX chicks coming and might save a roo or 2 this year. Or maybe just a handful of pullets again.
When they did 1st start laying we had a few egg issues (No shell or completely crushed but intact egg) but seem to be past that phase. Will probably only keep a layer for 1 season though so I do NOT run into health issues at older age. Have some eggs in bator but nothing was marked because everyone was free range laying at the time I set them for fertility check. 1 I know is CX layed because I watched her lay it and collected it immediately, and it is developing. Now I have them separated from flock for meat eggs.
I am doing this as a trial I been wanting to try for a few years. If it works out great. If not I am only out a couple dz eggs a week. And I have plenty coming now.