Ответ:
2. Mark has been playing football since he was in the kindergarten. He's been playing football for 9 years.
3. Mark has been riding the bike since he was 9. He's been riding the bike for 5 years.
4. Mark has been playing basketball since he was in 6th grade. He's been playing basketball for 2 years.
5. Mark has been playing computer games since he was 13. He's been playing computer games for a year.
6. Mark has been swimming since he was 9. He's been swimming for 5 years.
7. Mark has been cooking since he was 12. He's been cooking for 2 years.
Насчет 7 не уверена, непонятно, что он там делает.)