Bash script to verify modified date of file is within 24 hou

#!/usr/bin/env bash
#set -x

# Exit codes for OP5: 0, 1, 2 or 3 for OK, Warning, Critical or Unknown

NFS_DIR="/mnt/vol_nfs_nextgen_backup01"
BACKUPS=$(find "${NFS_DIR}" -type f -iname "*.tar.gz")
MAX_AGE=$(bc <<< '24*60*60')
declare -A OLD_FILES
declare -A ALERT


get_file_age(){
    for _FILE in $(echo "${BACKUPS}"); do
        FILE_AGE=$(($(date +%s) - $(stat -c '%Y' "${_FILE}")))
        FILE_NAME=$(awk -F'/' '{print $NF}' <<< "${_FILE}")

        if [[ ${FILE_AGE} -gt ${MAX_AGE} ]]; then
            # An old backup was found, adding to array
            FILE_AGE=$(date -d "now - ${FILE_AGE} seconds")
            OLD_FILES[$_FILE]="${FILE_AGE}"
        fi
    done
}


find_new_files(){
    for _BACKUP in "${!OLD_FILES[@]}"; do
        FILE_AGE=$(($(date +%s) - $(stat -c '%Y' "${_BACKUP}")))
        FILE_NAME=$(awk -F'/' '{print $NF}' <<< "${_BACKUP}")
        DIR_NAME="${_BACKUP//$FILE_NAME/}"
        NEW_FILES=$(find "${DIR_NAME}" -type f -mtime -1 -ls)

        if [[ ! -z "${NEW_FILES}" ]]; then
            # An old backup was found and no new backups were found in the same directory, adding to alert
            FILE_AGE=$(date -d "now - ${FILE_AGE} seconds")
            ALERT["${DIR_NAME}${FILE_NAME}"]="${FILE_AGE}"
        fi
    done
}


get_file_age || exit 3

if [[ ${#OLD_FILES[@]} -gt 0 ]]; then
    # An old backup was found, checking for newer backups in same directory
    find_new_files || exit 3

    if [[ ${#ALERT[@]} -gt 0 ]]; then
        # An old backup was found and no new backups were found in the same directory, printing alert
        for x in "${!ALERT[@]}"; do
            printf "%-30s %s\n" "${ALERT[$x]}" "$x"
        done
        exit 2
    fi

else
    # No issues found
    exit 0
fi