M3dusa,
The Creeps where never giving 1 field per 100 Creeps on insect. It was always the Incubator.
Before a recent change (1 month ago) the Incubator was giving 3 fields per level so the two examples you have were feasible.
Level 21 was giving in total 64 fields, and level 24 was giving 85 total fields.
Now the Incubator give 2 fields per level, which means 1 field available for other building.
This means that if you want to reach exactly those players, here it is:
For this you need: Incubator level 47, will give you the ability to build the same other structures and then destroy incubator to level 24

For this you need: Incubator level 46, will give you the ability to build the same other structures and then destroy incubator to level 21

If you want to do that within this lifetime

, you have to buy accelerators and probably resources!