I have an iPhone 3G. It has iOS 4.2.1 installed.
Is there any way I can run latest apps? It runs really slow.
there are always requirements to run a game/application on a device, if your device so not match the requirements then the experience will not great or not at all.
The latest apps require the latest iOS version.
I'm not sure you can get iOS 7 to run on an iPhone 3G but there are methods to jailbreak iOS 6 to run on older devices. However, if you consider your iPhone slow now it will only get worse with a later iOS version not intended to run on the device.
At the end of the day you have to face the fact that your iPhone 3G is a 5 year old device which in the electronics industry is very old and due to be replaced.