When to begin divesting your guns is not the same for everyone. But if you're still interested, and still looking to add guns, it's not the time to get rid of them. I'm hitting 70 this year, and no plans to give away most of my guns yet. I have given a couple to my oldest son and a couple to my youngest daughter, and her husband. Just guns that didn't need, and I knew they'd enjoy them more.
But the vast majority of my guns are still making me smile when I hold them, shoot them, or just look at them. So I'm not letting them go.
I have a master list inside one safe of every gun I own that lists serial numbers, and descriptions, plus any pertinent accessories that need to stay with the gun. It also lists what I paid for each gun so my heirs can have some reference. I don't update the values as it's not important they get more for them than what I paid. But in the case of some great bargains I got I have noted what their true values might be, so they have some reference beyond what I paid. I have a few historical guns that I've noted might go to museums if my heirs don't want them. I'd rather they were donated to a museum than simply sold to the highest bidder.
I think it's good to have some guidelines for your heirs, but shouldn't be so stringent that there's no options. Not all of my kids appreciate or even know zip about my old gun collection. So I'm not sure I want them to be burdened with me directing guns to them that they'd likely just sell anyway.