Despite his age, Lewandowski still makes a huge impact for Barça. He has a huge impact in every match he plays for Barcelona. If he were 10 years younger, Barça would be the same as they were during that unbeaten period. He's a truly exceptional striker. We know that his return to the team would clearly be a huge boost for Barça. Every player would want to work with someone as experienced as him.
Lewandowski can contribute a lot for Barcelona even he is very old as he is talented, skillful, experienced and very professional but no human and player can win against time and ageing effects forever. Barcelona can enjoy amazing contributions from Lewandowski until he hits his physical limits and has declining performances in both appearances and quality.
With a very old player like Lewandowski, that declining performances can appear anytime and can not be reverted, so Barcelona must have different plans and players as replacements on Lewandowski. If they struggle to replace him in one, two or three seasons, their performances and results can be affected a lot, then finance will be considerably affected negatively too.
Lewandowski was undoubtedly the best signing for Barcelona and so far, being a fairly old player, he has been performing at his best for Barcelona. A few seasons ago, there were rumors that Barcelona wanted to sell Lewandowski, but many criticized this rumor and many said that Barcelona won because of Lewandowski and if Barcelona sold him, Barcelona would not see victory again. However, a player cannot play for one club forever and the same is true for Lewandowski. Maybe Lewandowski will be seen wearing a Barcelona jersey for another season or two, but when he leaves Barcelona, who will take over the team in his place? Now Lamine Yamal may be playing well, but in the position that Lewandowski is playing, of course, a player as skilled as Lewandowski will have to be appointed to the Barcelona club, only then will Barcelona understand Lewandowski's absence.