so your boots are pretty old and the leather is harder then an old piece of bread. Stiff boots are bad for your feet because they dont give you the flexibility you need.Two ways to fix it and I have done both. Pros/cons of each one
1st is Lotion- regular hand lotion will work great but the problem is that it will only last a few days and you must keep applying it. Spread it all over the leather, if your leather is really dry then just rub it in like you would on your hands.
2nd way is virgin olive oil. Why not regular? Well because all I could find was virgin in the quick minutes I had. Spread it everywere and let it soak in. Virgin olive oil will last longer then loition and will help your boots in the water proofing department. Do not over do it in case it might leak through, just keep applying it until you are comfortable with the texture of the leather.
You can choose either of these two ways but to get the real color back after applying the lotion/oil to the leather, I recommend some Kiwi boot polish, just rub it on with a rag to help bring the color back. Some of you may say that they make special "mink oil" for boots and leathers. All that stuff is- is overpriced lotion. There is a boot shop near my house and they recommend lotion for super dry skin. After all; leather is just cow skin.....