If I've understood the rules, I *think* this would do the job, but it is a compicated thing to generate testcases for. Do you have any?

#! perl -slw
use strict;

my $polar    = 'DEHAW';        # Uniq E
my $charged    = 'DGYAH';        # Uniq Y
my $hydphb    = 'GAFIVL';        # Uniq FIVL

my $re_seq         = qr[
  # Capture
  (   
      # start char                                         
    [$polar$charged]   

      # Must contain motif                      
    (?= .* H[$hydphb][$polar][$hydphb]W .* )

      # Mustn't contain more than 4 polar chars
    (?! (?: .* [$polar] ){5} )

      # 18-24 polar|hydphb chars
      # Excludes the start and end chars (Adjust if wrong!)
    [$polar$hydphb]{18,24}    
      
      # # end char        
    [$polar$charged]                         
  )
]x;

while( <DATA> ) {
    chomp;
    print "\nTesting '$_'";
    s[\s+#.*$][];
    print "matched: '$1'" while m[$re_seq]g;
}


__DATA__
YVVVVVVVVVVHVEVWVVY                 # 1 too short
YVVVVVVVVVVHVEVWVVVY                 # min match
YVVVVVVVVVVHVEVWVVVVVVVVVY             # max match
YVVVVVVVVVVHVEVWVVVVVVVVVVY             # 1 too long
YVVVVVVVVVVHVEVWVVVVVVVVEY             # max polar
YVVVVVVVVVVHVEVWVVVVVVVEEY             # too many polar
YVVVVVVVVVVHVYVWVVVY                 # missing motif
[download]

Results

P:\test>junk

Testing 'YVVVVVVVVVVHVEVWVVY                            # 1 too short'

Testing 'YVVVVVVVVVVHVEVWVVVY                           # min match'
matched: 'YVVVVVVVVVVHVEVWVVVY'

Testing 'YVVVVVVVVVVHVEVWVVVVVVVVVY                     # max match'
matched: 'YVVVVVVVVVVHVEVWVVVVVVVVVY'

Testing 'YVVVVVVVVVVHVEVWVVVVVVVVVVY            # 1 too long'

Testing 'YVVVVVVVVVVHVEVWVVVVVVVVEY                     # max polar'
matched: 'YVVVVVVVVVVHVEVWVVVVVVVVEY'

Testing 'YVVVVVVVVVVHVEVWVVVVVVVEEY                     # too many pol
+ar'

Testing 'YVVVVVVVVVVHVYVWVVVY                           # missing moti
+f'
[download]

I make no predictions about efficiency:)