Kane has two options regarding his future, that is moving to Manchester United or playing for Real Madrid in La Liga. Kane will not have many guarantees of winning the title with Manchester United next season, but if he chooses Real Madrid then he might win it.
Kane is suitable as a successor to Benzema at Real Madrid, of course because Kane has a hunger to score goals. It's true that Real Madrid rarely sign players as old as Kane, but Kane should be a good short-term option because Real Madrid need a striker. But maybe, Real Madrid will also try to approach some other strikers who are younger than Kane.
Harry Kane has the opportunity to move to Real Madrid compared to Manchester United because there is news that the Spurs management will not release Harry Kane to a rival in the Premier League. Real Madrid and Manchester United are making efforts to secure the player's signature, but so far there has been no update regarding his future at Tottenham. But for the matter of titles at both Real Madrid and at Manchester United there is also no guarantee because next season's competition will probably be more competitive both in La Liga and in the Champions.
Harry Kane is a typical striker who has an eye for goal and he also has the ability to carry the ball from outside the box, so Real Madrid is the perfect place for him. But age is a problem Real Madrid can use his services as a short term option as you said and they can prepare another striker who is much younger than him.