Here are the rewritten sentences using "enough" instead of "too":

1. He is not old enough to wear this coloured shirt.
2. She is not strong enough to carry this bag.
3. This pen is not cheap enough for me to buy.
4. Bill is not wise enough to understand what I say.
5. This bag is not light enough for her to carry.
6. The test was not easy enough for them to do.
7. That sentence was not short enough for me to memorize.
8. The land is not fertile enough to grow crops.
9. The room is not quiet enough for us to study.
10. This book is not interesting enough to read.
11. We were not early enough to get good seats.
12. Jack is not hardworking enough to make progress in his study.
13. I’m not wealthy enough to help you with the money.
14. These oranges are not sweet enough for us to eat.
15. The shelf is not low enough for the boy to reach.
16. This road is not safe enough for her to go at night.
17. The water in this pool is not clean enough to drink.
18. Martha is not attractive enough to have a boyfriend.
19. This room is not bright enough for us to study.
20. He studied well enough to pass his exam.