Código para o Igão.

main.go

package main

import (
	"database/sql"
	"encoding/json"
	"fmt"
	"log"
	"net/http"

	_ "github.com/lib/pq"
)

type User struct {
	Name string `json:"name"`
	Age  int    `json:"age"`
}

type JSONBody struct {
	User `json:"user"`
}

type JSONResponse struct {
	Ok      bool   `json:"ok"`
	Message string `json:"message"`
}

func main() {
	db, err := sql.Open("postgres", "user=postgres password=postgres dbname=postgres")
	if err != nil {
		log.Fatal(err)
	}

	if err := db.Ping(); err != nil {
		log.Fatal(err)
	}

	mux := http.NewServeMux()

	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintf(w, "hello world")
	})

	mux.HandleFunc("/user", func(w http.ResponseWriter, r *http.Request) {
		if r.Method == "POST" {
			var js JSONBody
			dec := json.NewDecoder(r.Body)
			enc := json.NewEncoder(w)

			if err := dec.Decode(&js); err != nil {
				jsResp := JSONResponse{
					Ok:      false,
					Message: err.Error(),
				}
				if err = enc.Encode(&jsResp); err != nil {
					http.Error(w, "que porra é essa", http.StatusBadRequest)
					return
				}
			}

			var id int
			db.QueryRow("INSERT INTO USUARIO (name, age) VALUES ($1, $2) RETURNING ID", js.Name, js.Age).Scan(&id)

			jsResp := JSONResponse{
				Ok:      true,
				Message: "ok",
			}
			if err := enc.Encode(&jsResp); err != nil {
				http.Error(w, "que porra é essa", http.StatusBadRequest)
				return
			}
		}
	})

	http.ListenAndServe(":8080", mux)
}

/*

	var id int
	db.QueryRow("INSERT INTO USUARIO (name, age) VALUES ($1, $2) RETURNING ID", "bruno", 21).Scan(&id)

	rows, err := db.Query("SELECT name, age FROM Usuario WHERE id = $1", id)
	if err != nil {
		log.Fatal(err)
	}

	defer rows.Close()
	users := make([]User, 0)
	for rows.Next() {
		var user User
		err = rows.Scan(&user.name, &user.age)
		if err != nil {
			log.Fatal(err)
		}

		users = append(users, user)
	}

	fmt.Println(users)

*/