He's actually is

"But you told me earlier that you've reversed the aging process! Why can't I be immortal?"

"What makes you think I can't do both?" Jay shrugged. "Maybe you will age again once you receive more treatments. Or maybe I can give you some type of antidote."

John Doe considered what he'd learned so far. It seemed incredibly promising. But he knew that nothing in life came without risks. Still, he wanted more information before making a decision.

He glanced over at the children playing with their friends near the jungle gym. The boy seemed to be having fun. John wondered what it would be like to play with them someday. He yearned to frolic like a child once more. What would he do during those days? Would he attend school? Work?

Would he find love again?

He imagined meeting someone special, falling madly in love, getting married, having kids...

The idea excited him.