Thanks for this wonderful question. Let me dive straight to it.
The short answer is “blameless / perfect” in Gen 6:9 used is not the same as without sin / sinlessness of Jesus.
The Hebrew word for blameless/perfect (depending which version you are reading from) is Tammim, which could also mean complete or sound or sincere or integrity or upright.
Not just Noah, but Job was also called tammim in Job 1:1, 8, 2:3. Not only that, the same word was also used for the adversary himself, Satan as we know him, in Ezk 28:15. In classic Hebrew contrasting couplet: you were blameless/righteous (tammim) from the day you were created, until iniquity/unrighteousness was found in you.
Joshua gave an idea of what our word of the day means or is understood in ancient Israel’s times.
Joshua 24:14 NASB
Now, therefore, fear the Lord and serve Him in sincerity (tammim) and truth; and put away the gods which your fathers served beyond the River and in Egypt, and serve the Lord.
The pattern in which the Hebrew authors narrate tammim, is always paired with righteousness / upright / truthfully / faithfully / integrity (see also Psalm 37:37 besides the aforementioned verses), except when used for Satan, it was masterfully and, probably, intentionally contrasted with iniquity / unrighteousness.
And finally, it is topped with the coup de grace: fearing God and turning from evil, or serving Him, or walking with God.
One last thing to help us understand a bit more comprehensively. In Gen 25:27, the Bible says Jacob was a “peaceful”(footnoted: complete) man, living in his tents. The word tam of tammim(plural) was used.
The context used here is of course not blameless or perfect, but is about someone who is happy and content (complete) to stay home in his tents.
So, let’s put it all together, the word tam-mim, is therefore a state of completeness with God, where one delights himself in the Lord, and faithful to Him and His ways. Perfectly sound in His walk with God. In today’s term, it is akin to when we see someone who lives a pious and upright lives, we described him as a great “man of God”.
I hope that helps to understand a little Jewish perspective on a tammim man. (Okay, I promised the next point is really the last one) In fact the Jews treat being blameless (tammim) as a command in Deut 18:13 “you shall be blameless(tammim) before God”, so it is not treated as something unattainable.
Hope that answers your question. Blessings