system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does my 130 lb boxer/lab mix stay off the bed she has been sleeping on for 6 years if there is a 1 lb 7 week old kitten on it?

She will get as close as she can possibly get to it a lay down beside it.  She is not usually a meek dog.  She will bark at strangers (to her) entering the house and push me out of the way to get outside or what she wants.
gpt
Dogs are very aware of what a baby animal is, whether it be human, kitten, or otherwise. Most animals are keen on how fragile babies are, and will treat them very gently, or protect them- even outside of their species! Your dog knows that the kitten is just a baby, and needs to be given space. Your dog seems like he is taking special care to make sure the kitten is safe. 

Your dog may also think the kitten is his responsibility. You said it yourself. The kitten is sleeping on a bed your dog slept on for 6 years! That bed is his territory, it is a very big deal that he's allowed the kitten to sleep there. It is likely he will be protective of that cat for years to come.