Is it even possible?

Is it possible for a younger child to be toilet trained before the older one? Maybe it will happen in our family. Jayden has started to pull his diaper off when it starts sagging too much due to its saturation level. He doesn't like it, and requests a bum change. On occassion he will ask to sit on the potty, but nothing ever happens. He sees Ian do it and he always wants to do what Ian does.
Well, out of the blue, tonight he pulled his pants down and announced "pee-pee". Afraid he was planning on peeing on the floor I immediately pulled his pants up and asked him if we should change his bum. He nodded and said "mm-hmm" which is his prefered way of saying yes. Once we got to the bathroom though he says "pee-pee, potty!". So I plant him on the toilet and lo and behold he pees! Actually PEES! On the actual TOILET! I'm in awe. Ian has NEVER requested of his own free will to pee on the potty and actually do it. He's asked, when it's time for bed or other un-prefered activity. He's peed, when we've sat him on it and told him to go. But never have those to happy situations occured together. And tonight Jayden totally showed up Ian.
I made a really big deal about it with Jayden and broke open a brand new Hot Wheel for him. Ian immediately got jealous, but he can't have a new one until he starts pooping on the potty. We toyed with the punishment of taking away his old cars when he poos in his diaper but Ian just started handing them over voluntarily. We've read that punishment doesn't work but I guess we needed to find out for ourselves. We still haven't found anything that works to motivate Ian to say good-bye to diapers. Perhaps Jayden will...