1. There is no one-size-fits-all measurable way to determine what “good” means for everyone (though you surely could create one for yourself, but your “good” doesn’t apply to anyone but you).
2. Once you are good at said ability, you will need to keep doing it to remain good. It’s a universal law of nature: what doesn’t get used atrophies and dies. There is no finish line.
3. By the time you do become “good”, if your standards are high enough (which means it took a considerable amount of effort), you’ll be so invested in that skill that you’ll forget that you even had a date set for it.
4. People who are good — by whatever measure you choose — don’t take vacations from being good. That’s the only way they stay there.
So, how long does it take to become good?