Carol Vorderman was replaced because she wouldn't take a 90% pay cut - nothing to do with age. Rachel is well qualified to do the maths.
Alesha isn't qualified to judge dancing and she will not bring in the X-Factor fans - they'll still be watching X-Factor. I guarantee her snorting laugh will have got on everyone's nerves by week 2.
Why are old men allowed on TV and older women not? Yes, old/older was deliberate - Bruce is over 80 (old), but women usually get axed well before they're 60 (older).
Why should women have to put up with looking at old, ugly men on TV (considered mature by many, but usually just wrinkly), but men don't have to watch older, attractive women, many of whom get more attractive with age - Helen Mirren (63) being a very good example?
Remember we'll all be old one day. Younger people don't realise that the body might get older, but the brain remains at 26, and has experience and knowledge added that the young don't have.