You settle on the Physical Age setting. Your thumb hovers over the FastForward button. You feel a burst of adrenaline and take one last look at Randal.
Then you press the button.
The "+/- 0 years/second" moves up to "+0.1 years/second".
You watch Randal, anticipating the first signs of change. But, after a couple seconds, he looks more or less the same. You decide that 0.1 years/second isn't fast enough, so you press the FF button a couple more times until the rate is notched up to "+0.7 years/second". That's when the changes in Randal become more noticeable.
As his age ticks over from 23 through 24, 25, 26... You notice he seems to be...filling up. You see a noticeable paunch form under his shirt and his face begins to fill out. Also, his jaw-shadow darkens into stubble and a goatee forms around his mouth. The hair on his arms thickens as he enters his 30s. At the same time, his hairline begins to retreat.
Randal begins to notice these changes, and looks down, surprised as his stomach pushes at the insides of his shirt. He touches his face, surprised to find a goatee and thick stubble, which now seems to be turning into a full beard. He feels his head, only to find his hair is now almost gone. He stands up quickly, making surprised yelps.
As his girlfriend/fiancee/wife/whatever comes out from the bathroom, you decide you've had your fun and push the round button, halting the aging process, leaving Randal at 39 years, having aged him a total of 18 years.
Your work is done. You decide to try this out somewhere else. Maybe your friend would want to see it in action, too? Then again, you haven't been on such good terms lately. Maybe he could be the next test subject.
You ponder your next decision as an argument between a young woman in her early twenties and a man in his late thirties as the man tries to convince the woman of who he was, but the woman, convinced this was some sort of sick joke, demands to know where Randal is...