It's the last one that's the worst and his behaviour is giving you a bad example of what to expect in relationships. You are very much being infantalised and it can cripple someone. I know how this works - someone sounds very enthusiastic about you getting a promotion or doing some kind of positive life change but when they realise that you are serious they turn around and start saying things like 'Oh love, are you sure you can cope with that? Won't that be too much for you?'.
When you start spreading your wings and assert your independence, it is met with silences and subtle disapproval, enough to undermine your confidence, so you become less brave and your world becomes smaller. You are made to feel afraid of the outside world. You see the deal is this - either you submit yourself to their cage, or you are out on your own with little or no support. You won't be allowed to make mistakes. Even if you're super sensible and cautious as a person, if something bad happens to you or make a mistake, you'll be made to feel like a fool.
In his case the control could be a byproduct of his anxiety - that's how it often is with anxious people. Some manage it really well, but the way they comfort their own anxious feelings is first by controlling themselves (routine, things being done in a certain way each time) and then when that's not enough they control their external environment, and there's nothing more variable and anxiety inducing than people, with their own wills, desires, vulnerabilites and changing emotions. In that kind of environment they must know everything - they don't like you having too much privacy or secrets as that's anxiety inducing and you can't control something you don't know well and that has a mind of it's own.
Mind you, this could be mixed up with how he views women - how interesting and not surprising that your younger brother is allowed to do as he likes.
What is your mother doing in all of this? Is this not managing or is she also subjected to this?