They will let you fall to 20 for the most part. Below 50 you are at increased risk but below 20 is critical.
First why is your count so low? Has splenic involvement been ruled out? Or is it related to poor liver function?
In either case I cannot recommend enough that you go see a hematologist/onocologist before starting treatment and tell them your concern. Mine was indespensible and no way my GI would have done the same things.
Assuming no spleen issues, there are three ways used to increase platelet counts. Platelet infusion as needed. This is the simple and effective way. They are infused fast but does require going to a hospital. Second is corticosteroids like predisone. They prevent antibodies from eliminating platelets by surpressing the immune system. Contraindicated during treatment but so is bleeding to death. Their use is very short term and for emergency use. Finally there are at least three different medications, all injections from SQ to IV. All expensive and all have their own risks.
There are no vitamins or foods or herbs I know of that will do much in this case.
However even starting at 73 you still have a really good chance they will stay high enough to complete treatment.
Wish I had something better for you. Hope you do fine and best of luck.
Doug