There is a slang English phrase "young blood" which can be used in place of "you". When a person speaks to someone who is significantly younger, and wants to indicate that something this younger person did or is in the act of doing is immature and nonsensical, they can address the younger person as "young blood". Typically this phrase implies that the two people don't know each other intimately, like a parent and their child. Watch up to 3:06 of "Uncle Drew: Part 1" on youtube for example use cases of "young blood". How would you say "young blood" in Russian?
It depends on the level of how harsh ones want to sound. If the intention is just to indicate that somebody is too young and incompetent but by no means to offend, then
молодо-зелено will be the best choice, like in:
Эх, молодо-зелено, ты бы научился сначала токарным станком пользоваться, а потом уж лез.
Also, there's (quite rude) phrase
молоко на губах не обсохло.
But in you case I'd rather go with
молодёжь, like in
Эх, молодёжь, ну что, сразимся?
This is used exactly when you are slightly ironical but actually friendly.
Also, sometimes it's stressed differently -
мóлодежь just to sound bit more ironical.
One thing for sure - you should never ever try to translated it literally, since "молодая кровь" (or "свежая кровь") in Russian means something almost exactly different. It's about some fresh power, some younger and healthier forces that community needs to continue to evolve.
It is also worth noting that in Russian there is literally an idiom of "молодая кровь" (or "свежая кровь"), but its meaning is completely different even almost the opposite, positive, as we see. Meaning in the young strength and energy of someone, or the "reinforcements" of/for something ("влить молодую кровь")