Most people think that because they have 18 and more that it mean that they are adult and mature. That is something you must understand, being an adult and being mature is not the same thing and you must know that. Maturity come from when you realize that what you want is not good for you. That when you want something NOW it is bad for you. You realize that you have short term and long term options. That short term is what you want and long term is what you need. You decide to go for the long run and focus on what you need and ignore what you want. You work your patience and make it strong.
Get that understood before dating.