I think it is a pretty safe thing to say that there it is completely unrealistic that Bayern Munich will try to sign Cristiano Ronaldo, even if Lewandowski will leave the club and goes to Barcelona. There are several reasons for that. It would make absolutley no sense for Bayern to invest a lot of money into a player that is already 37 years old, even if we are talking about Cristiano Ronaldo here, he is still way past his prime in my opinion. Even if he would cost only around 20 Million € of transfer fee then he will demand a salary of at least 25 Million € per season i would guess because at the moment he gets around 30 Million per season at ManU AFTER taxes.
This is honestly the first time I have heard of such a transfer, there have not even been any rumours, I take it this is a fantasy? Why would he move to Bayern, in the German league? I think he would be bored there, even if he is in a strong team. And besides, the age, as you said, they will sell a younger player and take another one, who has a few more seasons to play?
The issue of Ronaldo joining Bayern Munich is indeed being discussed, both in print and electronic media, the rumor emerged after Lewandowski revealed that his era at Bayern Munich was over and he intended to look for a new challenge to another club.
Bayern Munich sporting director also opened up about rumors of Ronaldo joining Bayern Munich, there is no potential agreement between Ronalda and Bayern Munich even though Ronaldo is a top player, he ruled out Ronaldo transfer to the Allianz Arena.
So far Bayern Munich is very careful when bringing in players, Munich is always looking for players who can improve the club game. One of the reasons Bayern Munich put such a high price on Lewandowski is because they still believe in him, Bayern will do their best to keep Lewandowski so he can keep wearing the Bayern jersey and return to the training center with other players.