My age

Around Josiah's birthday he asked me how old I was. I told him that there was a good trick to remembering how old I am. I turned 30 just after you were born, so I am always 30 plus however old you are.
"How old does that make me?" I asked.
"35 because I am five."
"After your birthday how old will I be?"
"36 because I will be six."
"How old will I be when you are seven?"
"37."
"When you are eight?"
"38."
"When you are nine?"
39.
And how old will I be when you are ten?
Josiah looked at me with a sad look on his face and rubbed my hand.
"You will be 40, and almost dead."