For complying sample question, simply
sed 's/^# //' file
will suffice, but if there is a need to remove the comment only on some lines containing a particular regex, then you could use conditionnal address:
sed '/regex/s/^# //' file
So every lines containing regex will be uncomented (if line begin with a #)
... where regex could be [0-9] as:
sed '/[0-9]/s/^# //' file
will remove #  at begin of every  lines containing a number, or
sed '/[0-9]/s/^# \?//' file
to make first space not needed: #one two 12, or even
sed '/[0-9]$/s/^# //' file
will remove #  at begin of lines containing a number as last character. Then
sed '/12$/s/^# //' file
will remove #  at begin of lines ended by 12. Or
sed '/\b\(two\|three\)\b/s/^# //' file
will remove #  at begin of lines containing word two or three.
     
    
sed. I have made a significant change tot he Highest score answer (edits in review) and ask if @starryknight64 please review and choose an answer.