I believe rats, even when their homes have been wiped down and cleaned, still recognize their cage as home and can still get territorial, especially when a new rat enters the territory. I don't know how long you've been trying to introduce them, but it sounds like you're either moving along way too quickly, or that your older rat needs a neuter. If a rat is drawing blood, introductions have been done too quickly, or the other rat is too hormonal.
For now, I'd start over, having two separate cages close to each other where they can smell and see each other, but not so close that either rat (or their tails) can be injured. Stay in this stage until puffy fur, huffing (sounds like they're puffing air at each other), and any other aggression signs are nonresistant. Usually during this stage, when I'm sure both sets of rats are healthy and not able to get the other ones sick, I will transfer extra fleece and poo between the cages. Then the other rats smell each other, can learn about them on the chemical level, but in a safe manner.
Once that's gone well enough, I can begin introducing rats in neutral territory. Not in their play areas or in their cages. I often do the bath tub for this step. Also, make sure this space is large enough for both sets of rats to run around, escape from one another, etc. Confined spaces lead to stress and stress can lead to fights or rats picking on each other. People use the carrier method or the small space method, but I think that's dangerous and can lead to nasty fights or high tension. Plus, I wouldn't want to be shoved in a very small room with a person I barely know. People often recommend not intervening, but be prepared to separate the rats. Signs to look out for is puffy fur, aforementioned air puffing, chasing (like, persistent chasing that both rats are running at very high speeds), etc. I usually have hides small enough for the younger rats. If I feel the younger/newer rats are being harassed too much, I end the meeting and try again later. People say so long as there's no blood, everything's fine, but I believe there are times where babies or new rats have been stressed enough and it's time to end the session early.
When the time does come for everyone to move into the same cage, this is when I'm 100% sure there haven't been any signs of aggression for some time, I will go through a DEEP cleaning of the "main" cage and then set all of the rats inside. Then I monitor for a few hours, ready to separate or intervene as needed. This may be the loudest step, as rats squeak to communicate and little dominance tussles are needed for a hierarchy to be established.
Both of these steps can take many, many weeks to complete. Don't rush it at all. Some of these steps may not be passable until the older, more aggressive rat is neutered either.