With grep:
grep -E '^[#!]|.{4}'
That is, select lines that either start with # or ! or contain a sequence of 4 characters.
Or with awk:
awk '/^[#!]/ || length >= 4'
Or with sed:
sed -e '/^[#!]/b' -e '/.\{4\}/!d'
Stéphane Chazelas
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