The love story for me was the nature of the love and not the age of the lovers.
The moment somebody says 'this is very risky' is the moment it becomes attractive to me.
No one in the whole movie ever asks anyone, Did you write this letter' Part of the reason is that no one wants to hear that it isn't for them. As soon as they read it, they want it to be theirs.
The best preparation for acting is life -- observing life and people and observing yourself. All that becomes your library. So when you have to research a part, a scene or an emotion, you go into the library and get what you need.