For starters, if you are truly looking for a professional position anywhere, doing anything, please do not use words like "wanna." I promise you that will get your resume/cover letter promptly tossed. Recruiters and HR professionals have mountains of candidates to sift through, don't give them a reason to dismiss you before they even get to see what you can do. Also, when referring to yourself, "I" should always be capitalized. I know what your wrote may be acceptable for informal texts between friends, but you are not texting now, and you are in a professional forum looking for a professional position. Instead of typing or saying "i wanna," please replace it with "I want to." Never use slang when looking for a job. Ever. Period.
Recruiters and interviewers will make snap decisions about you, your work ethic, your intelligence level, and your professionalism based on what little info they have about you. Whether or not you agree, thinks it is wrong, or just unfair, that is the way it is. If you think I am being hard on you, it is better to hear that from me, here, than lose out on a job over it. I'm sure if you chose software development you must have a proficiency for it, as well as other STEM related subjects. That probably means you are quite intelligent and driven. What a shame it would be to be dismissed outright over grammar. Make sure the package you present, always, is polished.
With that said, 4 years of experience means just what it sounds like. They want the person that applies for this job to have 4 years of real-world, practical experience writing software in a professional capacity. If that's not you, then this position isn't for you at this time. Try to find opportunities to get experience like an internship at a software development company.