Whenever you feel you are ready. Best is what's best for You. If you have doubts, do a MSC. Some had to wait until divorced. I got mine at 22. I personally think about 24. But, some "mature" enough at 15 1/2. Some Never grow up.
After a long hiatus, I started riding, again. Now, That was Scarey. I had started on a Honda 50 at 22. Then, I suddenly got on a CB650 NightMare at 55..
I rode my Hondas and Triumphs at 55 in my '20's. Now I do 80 on my FXDL at 62.