Our two rats are one year old, we have had them about 10 months. My daughter tried to teach them a bunch of tricks in the beginning - "spin", "jump" (on to your hand), "tunnel" (through a duct tape roll), "stay", "roll over". At one point they were able to do each of those occasionally on command (with temptation of treats of course). But it has been several months since we "drilled" them, now they can only consistently do "spin" where they just do a 360 spin around. Both of them don't seem to really answer to their names. These are our first pet rats ever, so I don't know if they are smart/average/not so smart.
As with any animal you must constantly reinforce a desirable behaviour - how often depends on the species and individual. Personally, with my girls, I have found that every other day is good and I can easily introduce new movements through repetition and reinforcement. So you do need to be consistent with it and really reinforce - tasty, high-value treats and verbal praise. This reinforcement can be reduced as they become more familiar with a command.
Another thing to bear in mind is that males and females have different priorities - females tend to be very busy, active and interested whereas males are often more lazy, cuddly and laid back. Of course, there are exceptions to these extremely generalised rules. But you can see how the female persona would be more likely to engage in trick training!
I've found the spin command to be the easiest for a) the rat to pick up and b) for me to teach (easy hand signal!) which is likely why they have retained this one. I, personally, often go back to spin when teaching a new trick to give the rat an "easy win" and give them some encouragement without giving away rewards "for free" if you get me.
Recall takes more time and reinforcement than most tricks. To pull them away from anything that they're doing at any given time is a big ask, so they need to be sure that something REALLY good awaits them. I also ended up calling all of my rats to a sound (a clucking noise) rather than names - you can choose which one you want when they all arrive!
I think if you can get the boys motivated and interested and if you can repeat the training with plenty of patience that they will catch on very quickly. The main thing here will be making it worth their while .
In my opinion, rats are very smart, but it's whether they WANT to learn that influences things like learning tricks - not unlike humans!