Most Helpful Guy
It will be tricky, that's pretty big, but totally doable. Make sure that communication if very good, you will have different 'languages', you will have different ways of seeing things, so you will have to overcome miscommunication a lot. So stay calm. Make sure your voice is heard and respected.
Don't worry about people saying most relationships with big gaps don't last... because most relationships with small gaps don't last either. And a heck of a lot of relationships that get all the way to marriage don't even last. So... who cares about that. This is about what is good for you as a person right now, what will make you happy in life, and what will help you grow as a person.
Most Helpful Girl
You are at very different stages of your life. He has been through a lot in his life while you have barely begun to experience adult life. People can say that it's just a number but it's really not, it's experience. 18 and 38 is a hell of a lot different then 45 and 65 even though both are 20 years apart.