My 103-year-old grandmother’s adviser bought 5 bank stocks. She lost $300,000. Can I sue?

Dear Quentin,

I am the trustee/executor for my 103-year-old grandmother. She is alive and mostly doing fine. Lately, she has been allowing me access to her finances so there are no surprises when she dies. 

I just reviewed her investment-account statements and found that her adviser bought hundreds of thousands of…