I think if you stick to low fat meats and meat as a garnish or addition to main dishes based on some other central ingredient, rather than making it the center of the meal, you have less risk of overloading your system with animal fats that make you ill. Any major change in diet can cause digestive difficulties at first, but I doubt the human body would be unable to digest the proteins of meat even after a long period away from it. I think the excessive fat is the major danger from the point of view of starting to eat meat again.
I don't eat much meat and have learned that eating a whole sausage or a home-made hamburger (which is usually the kind with the juiciest fat) will make me quite ill. According to my doc, fatty meats like these are just too rich, and if you're not used to them, they can make your gall bladder or other parts of your digestive process go haywire. Beef and lamb are the usual culprits but duck, the fattiest poultry, can do it as well. I also think factory-farmed meat has all kinds of drugs in it so I won't eat that. In the U.S. that leaves very expensive specialty organic meat, which is too expensive to eat a lot of anyway. For those with chronic iron deficiencies (that's me) only a little meat a week will give you all you need; same for the needed amino acids.
I'm married to a vegetarian of 30+ years standing. We eat fish a couple of times a week - he avoids factory-farmed, but it is not always easy to do so- but we get most of our protein from non-animal sources. If you do the same I think you shouldn't have to much trouble getting used to a bit of meat again.