What even is technology?

I was just thinking about the time travel stories, and realized, that there is one strange question I cannot answer.

How do you decide what year does a technology become "manafacturable".

This question might sound strange, but if you give a renesance age emperor a detailed plan of a modern computer, he cannot manafacture it no matter how much detail you give to him.

On the other hand, if you give medieval king a detailed plans of an airplane, there is a chance that 10 smiths might be able to eventually manafacture one...

There are so many technologies, that I simply wander what was the last technology needed to create it...

Why am I even wasting my brain power on this shit?