My daughter was ready for first solo at the age of 14 after 8.5 hours at a country airfield. Her training was then slowed down and she went out and conitnued on with other flight sequences and finally went solo on her 16th birthday having done 22 hours.I must say that as a parent, I was very happy that she experienced more advanced flying sequences before first solo. I know of several young people who commence training and aim to go solo on their 16th and when they have reached the point of where the Instructor was prepared to send them off, they continue on with other sequences such as cross wind circuits etc. This has not added to the dual time it takes them to get their GFPT which still takes around the same time as the old restricted PPL (33 to 40hrs).
Yes, I agree it does take females longer to go first solo and if you read the AAUP latest newsletter, you will see an article about brainspace and the fact that older brains don't have as much of it - so it should follow that the older student will take longer to go solo except where they have previous aviation experience.