I use a similar pattern to find newest and oldest
PATTERN is any valid filename pattern and path if needed
PATTERN=*.txt          #Text file in current direcory               
PATTERN=/dir1/*.sh  #sh file in /dir1              
PATTERN=/dir2/[a-j]* #file beginning with a-j in /dir2

#Find Newest
NewFile=$(dir -1tQ ${PATTERN} | head -n 1)
NewFile=${NewFile//\"/}  #Remove " in Name

#Find Oldest
OldFile=$(dir -1rtQ ${PATTERN} | head -n 1)
OldFile=${OldFile//\"/}  #Remove " in Name