Ellipticals are larger than spirals. Elliptical Galaxies tend to be round or oval. No new stars can form in elliptical galaxies because all the fresh gas has been used. Concluding that elliptical galaxies can no longer form new stars, they must house very old stars. These types of galaxies stopped forming over 10 billion years ago.
Irregular galaxies have no specific shape.
In essence, they are what they are. They, too, still have gas to be used and therefore still form stars and house young stars. A galaxy is a large assembly of gas, dust, and lots of stars. They come in clusters of dozens to thousands that are over 15 billion years old. Earth and humanity are one, little, tiny speck on the huge black canvass of the Universe.