I can't get into cerulean cave. Can someone help me?

9/10, I like most of the Pokemon and their strong. But they can be stronger! Just kidding.

Yes I can help you. It's not easy at all. You don't just have to catch Mewtwo but you have to bring the Ruby and Sapphire to that professor at island one whose reapairing a machine. When you find the ruby and brought it to that professor, he gives you a second ticket, so you can go to island 4,5,6,7. To find the ruby defeat the pok�monleague one or two times(I don't remember) and at island one is something happened. There's a cave been opened. Where is that cave?? Well, there where the two boys of Team Rocket are, there's now the new cave. You have to defeat the rocket boys. It's an easy way to find the ruby.( I don't remember the way to the sapphire i'm sorry!) but you will get him easily. Good luck. Hope this helpss.
Greetzz :-)

You have to beat the Pokemon league and help Celio get the Ruby and Sapphire.

Yep. Defeat the E4, get the National Pokedex, defeat Team Rocket at their Warehouse and defeat the E4 again. Once you'vedone all this, you'll be allowed to enter.