Pyramidian

There is nothing legally wrong with your plan....
 
But...
 
As said before, you may have trouble convincing a suspicious adjudicator that you are marrying for love.
Think about it objectively. You've lived in the US for 9 years, almost half your life, and presumably have no wish to live back in the Philippines. And suddenly, just before you're due to leave, you meet, fall in love and plan to marry all within a very short period of time. 
This sort of thing might happen all the time in movies, but Hollywood and real life are different things.
 
Did you know your fiance for long before you started dating? 
 
 

Although overstays are forgiven for spouses of USCs, in today's climate, I wouldn't risk staying illegally in the US. Deportation is always hanging over those here illegally.
 
Either marry and take your chances with the AOS or leave the US and continue your relationship, then either do the K-1 or marry and do the CR-1 a bit down the road. 
 
If you're going with AOS, at least wait to get married until November, so you've been together at least six months before tying the knot.

There is nothing wrong in living with his parents if they approve you living with them till you get an apartment of your own. You can wait till November and get married, even if you file your AOS a date before your 22 birthday, your new AOS will cover your legal status till the process is over. Getting married to him and not living together or knowing him that much is an early cause for martial disaster not to mention USCIS. 
My advice is first, concentrate on your love life, make that strong, get to know each other. Your overstay shouldn't be a priority right now as a USC covers that if your marriage is bonafide. 
Stay strong and focus on making your happiness a priority. When time to file and fill out paperworks, VJ family is here to help you. Go through the guide in this forum and you will see everything you need from Start to Finish.
good luck