Best way to store data in BoltDB

Yes, I would recommend marshaling the User struct to JSON and then use a unique key []byte slice. Don't forget that marshaling to JSON only includes the exported struct fields, so you'll need to change your struct as shown below.

For another example, see the BoltDB GitHub page.

type User struct {
    Name string
    Age  int
    Location string
    Password string
    Address string 
}

func (user *User) save(db *bolt.DB) error {
    // Store the user model in the user bucket using the username as the key.
    err := db.Update(func(tx *bolt.Tx) error {
        b, err := tx.CreateBucketIfNotExists(usersBucket)
        if err != nil {
            return err
        }    

        encoded, err := json.Marshal(user)
        if err != nil {
            return err
        }
        return b.Put([]byte(user.Name), encoded)
    })
    return err
}

A good option is the Storm package, which allows for exactly what you are wanting to do:

package main

import (
   "fmt"
   "github.com/asdine/storm/v3"
)

type user struct {
   ID int `storm:"increment"`
   address string
   age int
}

func main() {
   db, e := storm.Open("storm.db")
   if e != nil {
      panic(e)
   }
   defer db.Close()
   u := user{address: "123 Main St", age: 18}
   db.Save(&u)
   fmt.Printf("%+v\n", u) // {ID:1 address:123 Main St age:18}
}

As you can see, you don't have to worry about marshalling, it takes care of it for you. By default it uses JSON, but you can configure it to use GOB or others as well:

https://github.com/asdine/storm