Tottenham also have quite many centre-backs now but I can't say their defense is very solid now. Maybe they want to get rid of at least one of the current players and bring a credible one to the team.
I think Rudiger is happy in the Real Madrid squad. I think it is unlikely that he will go to another team from Real Madrid. They may have to pay a huge fee to Real Madrid to get him. Considering that he is 29 years old, I don't think Real Madrid would want to spoil a position where they won't have problems for a few years.
I think that Rudiger would definitely want to stay and Real Madrid will be fine with it. Even if they are planning to make their squad younger over the coming years, you usually want to have some balance between older, experienced players and younger players especially in the defense lines. Experienced players do have a couple of tricks up their sleeves to shut down a strong offensive opponent. I would say that very young defenders are more prone to mistakes in certain situations.