"It's crept up on me a little bit. I'm really excited about it and it's a milestone I'm very proud to reach," said Pennell.
"If I had managed to stay fit in these last few years it would have come a lot sooner but I'm delighted the day has finally arrived."
Pennell has enjoyed one of his most successful seasons in a Warriors shirt this campaign and claimed his solitary try as he opened the scoring when his side battled to a bonus-point victory over London Wasps last month.
The full-back has played 22 games this season and was rewarded for his impressive form with a new contract in January.
He continued: "I was delighted to sign a new contract this year. I've come through the club's academy so I wouldn't want to be anywhere else."
With Warriors looking for their sixth league win of the season against third-placed Harlequins, Pennell admits he would love to mark his century game with victory.
He added: "We'll be putting everything we have into this game and we're looking forward to it. We have been focused on putting in a good performance in front of our home supporters.
"I'm really proud to have played so many games for my hometown club and hopefully I will play many more games. It makes it even more exciting to think that I'll be reaching the milestone at Sixways."
Limited tickets for Saturday's match against Harlequins will be available at the gate. To avoid long queues and potential disappointment buy tickets now by calling 01905 454183 or clicking here.