Kyle Shanahan emphasized the importance of having a veteran like Trent Williams on the team with a bunch of young players.

"I would love to play until I'm 40," Williams recently said from 49ers minicamp. "I would love to make it into that special group. But if it's not in my cards, it's not in my card

For now, San Francisco 49ers offensive tackle Trent Williams doesn't know when he's going to retire, and he pretty much plans to keep playing until the wheels fall off.