Mick Jagger might be old for a father, but in his old age he has settled down and is ready to take care of a child. He may not be able to be as involved or as hands on as some young fathers, but he will have more time and can spend time with his child.
The great thing about being rich is that you can do whatever you want. Mick Jagger and his 29 year old girlfriend are about to have a baby. Mick is a great grandfather so he's been down this block before. He is still a rocker so more than likely he will employ many nannies to take care of this new child.
Mick Jagger, along with many males worldwide has the right to be a father. As a father to seven children already, he has experience in childcare and plenty of financial support for his children. The expected child is the first between Jagger and his current partner and by saying Jagger is not 'ready' to be a father is depriving his partner of the chance at motherhood herself.
Even though he is old, I don't believe that Mick Jagger is ready to be a father. He is living a celebrity life that is filled with parties, drinking, and plenty of attention. A child needs to grow up in a more stable environment than this to become a stable adult.