turkey loads
As noted, the age of your gun is not an issue, it will be plenty safe with modern ammo, provided it is in safe condition to begin with.
I've not read as to whether or not your gun has 3" chambers, or simply 2-3/4", can you advise further?
A fixed "modified" choke is usually considered a bit open for turkeys, but.......there is an answer to that issue these days. If your gun does indeed have 3" chambers, there is a relatively new lead shotgun load, reasonably priced, that will most likely allow your gun to shoot "full" patterns with no modifications. The load is Winchesters XR "Longbeard" turkey load, and I buy mine at Walmart. Longbeard is without a doubt, the best performing lead load on the market to date. I believe they are only made in 3" length.
If your gun is 2-3/4 chambered, look for "short magnums", 2-3/4" shells throwing more shot than standard field loads, ususally in the 1-1/2 oz range for 12 gauge. All the major ammo company's have a short mag, baby mag 12 ga load. Although I'm a #5 shot man myself these days, for a modified gun that I was trying to "tighten up" for turkeys, I'd consider #6 shot first due to the higher pellet count per payload.
Irregardless, pattern the rig to see how it does at turkey ranges, say 30-35 yds. If you can arrange some better sight arrangement than a simple single beadbead, (at minimum 2 beads, at best an adjustable sight like for slugs, a dot, optic, etc) I highly recommend it.