In order to successfully saddle up and ask your horse to carry weight you have to expose the horse to everything that they are going to need for this experience.
Can you yield your horse? Have you exposed your horse to the tools; tarp, bag, balls, etc.? Can you longe your horse? Can you ground drive your horse? How is your horse’s posture? Can your horse stand still and calm? If you answered no to any of these then you’re not ready to get on. But, you should be getting ready.
How do you know when you’re ready to get on? The horse is going to tell you. By this we mean that the horse will have been exposed to enough situations that this will just be another exercise. Your horse must have a good posture, be calm and relaxed. Don’t put a time limit on this. Don’t wake up tomorrow and say "Well, my horse is two I better get on today". Can you bring your horse up to you while you are above them and practice throwing a leg over without having the horse run off?