Clark's response, should cover most of what you need right now.
If you continue to train for 10 years and your friend does not, then the 'friendly fights' will either become one sided or evaporate completely as you lose interest in the win/lose paradigm of fighting.
Over time in aikido you may realise that the only opponent worth grappling with is oneself. You will provide yourself with many opportunities and almost limitless material to work with.
Friends are for having a good time with, what happens when you do get to the point when you can 'beat' him, will it change the nature of the relationship? will you feel superior to him? will he be pleased for you?
Fighting is such a 'gross' level of human interaction, there are better ways to go about things. Aikido practiced long enough provides the skills to deal with combat effectively. The more you practice the less you want to engage in combat to test your skills. Practice the art for it's own sake, the rewards come slowly, and are dependant on your own integration of the aikido principles into your own life.
Take you mate down the pub, buy him a drink, and have a laugh together, harmony in action