Dr. Who Season 5 2010

I have been watching the new season of Dr. Who this past week. It opens up where season 4 ended, the doctor transformers along with his tardis. the 4th season was taking place in 2010. Season 5 picks up right where 4 left off, 2010. The Doctor meets a 7 year old Amy. She needs help, her parents have passed away and all she has is an Aunt who is not around, and there is a tear forming in her room. The Doctors tries to help and goes back to the tardis.   He tells her he will be right back and enters the tardis, he ends up returning 12 years later, Amy is now 19. He then leaves her again and returns 2 years later, she is now 21. If she was 7 in 2010, and we are now dealing with a 21 year old Amy, it would now be the year 2024. But, a few episodes later the doctor takes her to the future of, 2020. There has been a time line screw up. I don;t think the writers realized that if he met Amy in 2010 at 7, then left and returned when she is 21, it would no longer be 2010, and the future would not be 2020 any longer. Whoops.