age does have an affect...but honestly I don't think its really all on him. I'm 25, and have been dating my girlfriend since she was 19 (she's 21 now). and although it isn't as big of a difference, It's enough of one. when one or the other is young dating an older person, the older person sometimes gets thrown into a "parent" position. not because they want to, but because they've had more experiences, it almost comes naturally. and of course when someone is in their mid to late teens, theres usually a big aversion to parent types. this is a big clash right here...
the other reason I'm offering has nothing to do with age. by the time a relationship reaches a year...the newness has worn off, the excitement of having another person isn't so incredibly exciting anymore. so you start to find stuff about the other person that bugs you, and you are comfortable enough with that person to let him/her know it...and viola...you have an argument..
neither one of these is a sign of doom....provided that both of you realize that you do love each other, and both of you have the patience, and think clearly enough to not do anything over the top to the other. I honestly think you're going through the biggest test of a relationship...if you pass it, then everything will be alot smoother in the future...if you dont...then maybe it wasn't meant to be