A/N: A more likely explanation than the one given in Last of the Time Lords.
.oOo.
"What the…?"
Jack would be doing his hair about this time. That meant he had probably spotted it.
"Ianto, I'm going grey!"
He had. Ianto sighed and crossed to the bathroom, deliberately slowly. As expected, Jack was in front of the mirror.
"Look!"
Ianto grinned and shrugged. "So?"
"I'm aging."
Ianto tried not to laugh. "It's normal for guys your physical age. You were about forty?"
Jack feigned insult, failed miserably. "Yeah."
"Then it's normal. I wouldn't worry."
"I never used to get them."
Ianto hugged him from behind. "You never used to have to deal with Gwen and Owen."