There are not too old when looking Modric and Karim Benzema contribution for Real Madrid exactly last el clasico match when success eliminating Barcelona in semifinal Copa Del Rey. Look how effective with Luca Modric movement in midfielder area and success with beautiful assist for Karim Benzema scoring goals.
For Karim Benzema is most complicated as forward, he not only success with goals contribution but also he can play well with assists contributing for Vinicius Jr goals, Karim Benzema is not the typical selfish player and more priority with the other player if have good position or chance for scoring goals than push by him self how to score, become twice in a row Karim Benzema success with hattrick and waiting next match will consistent scoring goals again?
For the skills or quality, they are surely not too old. Age doesn't give a significant impact on their skills/quality. I agree that Benzema and Modric still can play effectively, even if it is in the current El Classico. But age must affect the fitness or endurance of the players. We all know that Benzema often got an injured problem, while Modric can't play full-time as previously. For the whole season, Real Madrid can't rely on these players anymore since Real Madrid plays in some big competitions that possibly make the old players feel tired or get injured. So, I really support the idea that the old players in Real Madrid need proper successors for the next season. For the midfield line, there are already many young players. But for the attacking line, there is still no option for Benzema's successor (pure CF position).