I've worked with leather for 40 odd years, both professionally and for fun.
Properly maintained good leather can last several lifetimes. But, once it is allowed to dry out and become brittle there is only so much you can do with it.
Lexol Leather conditioner is one of my favorite products. It's easy to use and won't generally leave an oily residue. Pure Neatsfoot oil is easy to over do and will tend to leave an oily feel to leather. Beeswax is also a good product to use.
When trying to "restore" old and dry leather go slow with the conditioners, apply a little at a time and let it soak in.