What do the 2nd and the 3rd paragraphs mean?
Ajit Jain heads up BH Reinsurance and has done wonders, building float to an incredible $24 billion as of year-end 2008. What would Berkshire do without him?
Buffett noted that the authority here goes with the person, not the position.
While he’s happy to give his pen to Ajit, signing for major deals, he would not do so with anyone else.

Question

Answer

1. = Ajit Jain who is in charge of BH Reinsurance, has done a magnificent job. Starting with a "float" an ending up with $24 Billion at end of the year 2008. (next part is a question) What ? would the Company do without Him.
"a float" I assume is the "start up capital" or a set amount of money that he had available. or it probably means the day the company was "floated on the stock exchange" The day the company was first made into a shareholders company.
2. = Buffet noted the the success is due to the personality "the person" not the position of power. He Buffet is happy for Ajit to sign major deals, because Ajit is competent. he would not give this responsibility to another person.

It would be easier to answer questions if you gave more context. I am assuming Buffet is a person and Berkshire is a Company.