Hi. Yes, this a common occurrence among people with AD/HD; acting "younger" than their age. Many people with AD/HD are seen as "immature" or "silly" because the brain lags behind by a few years than people their age.
Also, emotional dysregulation is a common issue in people with AD/HD, as it is a type of executive function, which seems to be a main problem in people with AD/HD, and why people are seeing it more as a learning disability than before. Executive functions are what control several aspects of your brain and are like the headquarters for other functions like working memory, inhibition, flexibility, metacognition, and etc..
Emotional dysregulation is when you can not control your emotions appropriately for the given situation, whether it is anger, sadness, excitement, or other emotions.
Also, if you believe you do have AD/HD, look up AD/HD specialist in your area, and ask to get an assessment by someone who knows AD/HD. They will be the right people to determine whether or not you have AD/HD. Also, you can look up different strategies to implement in the meantime, such as organizing your time, organizing your house, making lists, and planning things on a calendar, whether that is a physical calendar or a phone app.
Some pdocs and therapists don't understand AD/HD, and believe it is not a real condition, and just a way for kids to get drugs to get high or have an advantage of people (lack of sleep, extreme concentration). But with people with AD/HD, this just allows them to be on the same playing field.
I suggest you look up information on the internet regarding AD/HD, and I wish you the best of luck in finding someone who knows AD/HD.