okay i know i am going to get hate for this. but .. spike is older than sweetie belle. if we establish that twilight is around 20 years old. and its shown that she got her cutie mark when she was younger than the CMC , lets say at the age of 5 .. that means that spike is at the least 15 years old. and sweetie belle is around 8 years old... spike is immature for his age. giving that he has been raised as a baby dragon. but since dragons live for hundreds if not thousands of years . 15 years would be considered a baby to them. also.. if we are going to go with the whole . spike needs to be with somepony of his age... why pair him with sweetie belle.. that's demeaning to sweetie.. imagine the only reason spike is dating her. its because he couldnt get with rarity. so instead of getting the gold. he will just settle down for the silver.. im sorry but i dont think thats fair for sweetie belle at all..