Can you get alzheimer's at 19years old im scared i have it?

ive been forgetful lately and well im scared something might be wrong im not a forgetful person people around me tell me im fine but im still worryed can you get early onset alzheimer's at 19 years old or can people in there 20s get it ? my great granma alzheimer's had when she was in her 70s im scared im gonna end up like her im also very stressed and i havent been sleeping very well and i have osd is all of this in my head or do i need to be worryed and what can i do to prevent getting alzheimer's later in life please help ps i have most of the sighns also i have autism please help