Springでビルドが失敗する

前提・実現したいこと

SpringとPostgreを連携させようとしたいのですが上手くいきません。
Postgreを入れてServiceやentityを作っている最中にビルドができなくなったので、連携時の何かが原因だと思いますが。。

発生している問題・エラーメッセージ

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2020-08-27 22:35:49.753 ERROR 5475 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'systemUserRepository' defined in com.example.demo.SystemUserRepository defined in @EnableJpaRepositories declared on JpaRepositoriesRegistrar.EnableJpaRepositoriesConfiguration: Cannot resolve reference to bean 'jpaMappingContext' while setting bean property 'mappingContext'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jpaMappingContext': Invocation of init method failed; nested exception is org.hibernate.AnnotationException: No identifier specified for entity: com.example.demo.SystemUser

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jpaMappingContext': Invocation of init method failed; nested exception is org.hibernate.AnnotationException: No identifier specified for entity: com.example.demo.SystemUser

該当のソースコード

package com.example.demo;

import java.util.List;

import javax.servlet.http.HttpSession;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
public class HelloController {

    @Autowired
    private SystemUserService userService;

    @RequestMapping(value = "/")
    private String index() {
        return "index";
    }

    @RequestMapping(value = "/form/edit")
    private String edit() {
        return "/form/edit";
    }

    @RequestMapping("/form/editCheck")
    public String editCheck(@ModelAttribute("form") Form form) {

        return "/form/editCheck";
    }

    @RequestMapping("/form/finish")
    public String finish(HttpSession session) {
        SystemUser sessionEditForm = (SystemUser) session.getAttribute("form");

        this.userService.save(sessionEditForm);

        return "/form/finish";
    }

    @RequestMapping(value = "/test", method = RequestMethod.GET)
    public List<SystemUser> test() {
        return userService.findAll();
    }

    @ModelAttribute
    Form setupForm() {
        return new Form();
    }

}

package com.example.demo;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Table;

import org.springframework.data.annotation.Id;


@Entity
@Table(name = "systemuser")
public class SystemUser {

      @Id
      @GeneratedValue(strategy=GenerationType.IDENTITY)
      @Column
      private int id;

      @Column
      private String name;

      @Column
      private int age;

      public int getId() {
        return id;
      }
      public void setId(int id) {
        this.id = id;
      }
      public String getName() {
        return name;
      }
      public void setName(String name) {
        this.name = name;
      }
      public int getAge() {
        return age;
      }
      public void setAge(int age) {
        this.age = age;
      }

}

package com.example.demo;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface SystemUserRepository extends JpaRepository<SystemUser, Integer> {



}

package com.example.demo;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
@Transactional
public class SystemUserService {

    @Autowired
    SystemUserRepository userRepositry;

    public SystemUser save(SystemUser entity) {

        return this.userRepositry.save(entity);
    }

    public List<SystemUser> findAll() {
        return userRepositry.findAll();
    }

}

spring.datasource.driver-class-name=org.postgresql.Driver
spring.datasource.url=jdbc:postgresql://localhost:5432/mydb
spring.datasource.username=username
spring.datasource.password=password

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.3.RELEASE</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <!-- データベースアクセス -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>

試したこと

テーブル作成時のSQLはこちらです。
CREATE TABLE systemuser (
id SERIAL NOT NULL,
age        INT,
name     VARCHAR(20)
);

補足情報（FW/ツールのバージョンなど）

ここにより詳細な情報を記載してください。