Is age really a factor?

Ok, So there’s this guy and he is 26 going on 27 in August and I just turned 18 in March but thing is I like him. Well we knew each other for about a year and he was just a friend a really nice and caring friend. He never showed any interest in me until now he says things like imma be his wife and how he loves me sooo much as a person. But I don’t know wether or not I should trust him at first i didn’t like him but now I find my self thinking about him and we never spend a day w/o talking to each other. He’s willing to do so much for me but I don’t know wether or not i really should trust him. My friends including my brother tells me that there is probably something wrong with him if he can’t find someone his own age to be with. But I don’t know I’m tired of feeling this way and I wanna know wether or not I should trust him being that there is a 9 year difference? Some one any one plz help. Because I realy think that I can marry this guy but I don’t wanna make a stupid decision and to tell you the truth I don’t find him attractive I really like him for who he is. Should I enter a relationship with this guy?