You should be ready to submit as soon as whatever you're writing is finished. You can't get published without submitting work, and the submission process is more than half the battle. Finishing work but not submitting it because you don't think you're ready is just not wise.
You'll probably never be ready until you learn to finish what you start, and to submit everything you finish.
Now, I don't think beta readers know any more than mothers, brothers, and the man in the moon, but if it makes you feel better, let others read it. Of course, it may make you feel worse, and everything they say is bad may be the same things an editor loves, but have at it.
But you'll gain absolutely nothing until you start putting your work in front of editors. You won't even have a clue whether the beta readers were right or wrong until you put the work in front of editors.
No one on earth can tell you something you write is publication ready except for the person who can write you a check. Your friends can't tell you, beta readers can't tell you, and you sure can't know yourself.