[p_ing]

Not all plastics are brittle, even after time. It is highly dependent on the plastic used.

[eldaisfish]

ok, now please explain whether any plastic is more or less brittle than aluminium.

[p_ing]

It's not.

That being said, aluminum will suffer from dents and scratches. Every material is a trade off. You're not going to pull a "gotcha" comment, here.