This is a good plan:
When your at your grand parents buy something is not expensive and you can have fun with it..
Like ps3 or some thingys in tb (About 1-300 $)

Later your older like 20 buy a Apartment and live there you still can visit your grand dad and grand mum (About idk lets say 5000 $)

Then when you got kids you maybe have to buy food for family ... (about 200+$ Everymonth (You better get a job lol))

Later you save some money when your with your children and buy them some presents so your a fine dad (Rest of money)

i think that would be a nice plan