Why does my boyfriend critcize me on the way I do things?

Guys typically have a "problem solver" mentality, and I'm sure that's all he's trying to do. But you should have an open conversation with him about his approach. Maybe the information he shares is very useful, but if he presents it in an authoritative manner, it doesn't seem like your boyfriend. It's more like he's the parent and you're the child, right?

So tell him that you appreciate him trying to help you, but that you need him to be supportive, not demanding.

If he can't handle that, then he's a controlling type personality, and he may not be the type of person you need in your life.

Update: It had to bother to a certain degree to post it, so I think it's good to take some time to think about what you want and what you can do. Then decide if you still want to have a conversation with him about this. I personally feel that talking about it will be helpful to the both of you.

Just because he's older does not mean he knows more or have the right to make you feel bad when you're doing things differently than what he would do. I think there is a good way of telling/showing other people's flaws. If it bothers you, I think you should talk to him about it if he does not already know it bothers you. How do you respond when he does that (e.g., nonverbals, verbals)?

Yes you should talk to him about it! and tell him, that if he likes you he should like you for who you are, not for what you could be if you were molded into his version of the perfect person. As much as you like this guy, by correcting you all the time he is being condescending, which means that he thinks he is smarter than you. This probably won't change either. Someone who really cares about you and has your best interests in mind would know that criticism breaks down your self confidence/ esteem. I would definetly tell him straight up how you feel, and don't let him tell you your silly for feeling that way. If things don't change fast, then get out- this kind of condescending behavior is only the beginning of a controlling and belittling relationship, and it will continue to get worse.