You never feel ready. But really the first 6 weeks is about learning on the job how they expect you to do things, and you seeing how that works in practice, it's not always the best way, but you can't change the system unless you understand why they do things they way they do. Hopefully, at that point you also start to feel comfortable in whatever the duties are. And you also get to see what your weaknesses are and can spend time ensuring you get better at those areas.
And I'm giving it to you from someone who changed to IT at a later stage. One of the best things is that you have life experience, and that makes all the difference in a lot of roles. You can understand the end user a little more, have diplomacy skills which I find lacking in a lot of IT support roles.
Personally I ended up doing Major Incident Management/Problem Management, but that's cause I hated studying, and things like Networking etc seem to what you to be forever studying. My life skills and big mouth suit that role well, and you get to work on everything in an organisation operations wise. ITIL is a good thing to learn just so you understand how things are supposed to work in an organisation.
Last time I was running a team, I really was looking to hire those that had done other things in life outside of IT. I found those people the best to have as they understood how things fit together much better for the end user and work wise, knew that IT was a pretty cushy job compared to other things you could be doing to earn a living.