Page limit for thank you letter to mentor of years?

Answer 1

One page would suffice.

Answer 2

A couple of lines is polite and perfectly adequate.  

A whole page is WAY too much.

Just say 'thank you', wish him or her well and leave it at that.

Answer 3

That doesn't sound like a thank you, that sounds like a look at me bio

Answer 4

not a page, just a simple thank you. No one wants a dissertation...