Everyone also knows that an athlete's performance will decline as they get older, but I think you can rethink your words. Look at the rating on their match yesterday, he played well with Joao Mario, Otavio & Wendell. Usually older players will be played for half game, but not Pepe, he played the full game. Arsenal still have the biggest opportunity to progress to the next round, but that doesn't mean we have to underestimate Porto, we'll see what will happen in the second leg. Honestly, I wouldn't bet on this match because I think it's too risky.
The quality and total productivity of almost every human declines with age and not just withe athletes or footballers so it's really something that we shouldn't see like a thing peculiar to athletes alone both every other person in their various field but they will have the advantage of been much more experienced than the younger ones.