AuthServiceProvider.php

<?php

namespace App\Providers;

use Illuminate\Foundation\Support\Providers\AuthServiceProvider as ServiceProvider;
use Illuminate\Support\Facades\Gate;

class AuthServiceProvider extends ServiceProvider
{
    /**
     * The policy mappings for the application.
     *
     * @var array
     */
    protected $policies = [
        'App\Model' => 'App\Policies\ModelPolicy',
        'App\Models\Post' => 'App\Policies\PostPolicy'
    ];

    /**
     * Register any authentication / authorization services.
     *
     * @return void
     */
    public function boot()
    {
        $this->registerPolicies();

        //
    }
}

PostController.php

<?php

namespace App\Http\Controllers\User;

use Illuminate\Http\Request;
use App\Http\Controllers\Controller;
use App\Models\Post;
use App\Http\Requests\PostFormRequest;
use Auth;
use App\User;

class PostController extends Controller
{

    public function __construct()
    {
        $this->authorizeResource(Post::class, 'Post');
    }

PostPolicy.php

<?php

namespace App\Policies;

use App\User;
use App\Models\Post;
use Illuminate\Auth\Access\HandlesAuthorization;

class PostPolicy
{
    use HandlesAuthorization;

    /**
     * Determine whether the user can view the Post.
     *
     * @param  \App\User  $user
     * @param  \App\Models\Post  $Post
     * @return mixed
     */
    public function view(User $user, Post $Post)
    {
        return $user->id === $Post->user_id;
    }

    /**
     * Determine whether the user can create Posts.
     *
     * @param  \App\User  $user
     * @return mixed
     */
    public function create(User $user)
    {
        //
    }

    /**
     * Determine whether the user can update the Post.
     *
     * @param  \App\User  $user
     * @param  \App\Models\Post  $Post
     * @return mixed
     */
    public function update(User $user, Post $Post)
    {
        //
    }

    /**
     * Determine whether the user can delete the Post.
     *
     * @param  \App\User  $user
     * @param  \App\Models\Post  $Post
     * @return mixed
     */
    public function delete(User $user, Post $Post)
    {
        //
    }

    /**
     * Determine whether the user can restore the Post.
     *
     * @param  \App\User  $user
     * @param  \App\Models\Post  $Post
     * @return mixed
     */
    public function restore(User $user, Post $Post)
    {
        //
    }

    /**
     * Determine whether the user can permanently delete the Post.
     *
     * @param  \App\User  $user
     * @param  \App\Models\Post  $Post
     * @return mixed
     */
    public function forceDelete(User $user, Post $Post)
    {
        //
    }
}

Como que estão suas rotas?