Is it too cold to go hiking without a hoodie when it’s 55 degrees and sunny?

I don't see it being a problem unless there is a strong North wind then it

may be a little cool.

55 isn't all that cold, especially if it's sunny. It depends on how acclimatized you are to the weather, and if your in good physical shape. Obese people tend to get cold easily. The sun will definitely help keep you warm, and physical activity will also help keep you warm.Wearing a hoodie can actually make you sweat if you are exerting yourself by walking, and especially hiking, which implies walking over rough terrain.

After you warm up you will probably want to take it off, but I'd bring it anyways in case you get lost and need it that night. 

Start with it on, and take it off if you find yourself heating up too much. Better to have it just in case.

Wind counts in this one, a 20mph breeze can make it seem a bit chilly. Also, hiking is often in the woods, not actually sunny in there, so temp drops.

That's nearly 13 degrees, of course it is! British summers don't get much warmer than that 😂

Surely you can make that decision yourself.