I am aware of a gemara that puts Levi at age 13 at the time of the maaseh Shechem, but I would ask you to cite a source that puts Dinah at age 3. If you will recall, at the time of the incident where Yaacov met Eisav, his youngest son (Yosef) was 6-7 years old (we know this because Binyomin was in utero). Dinah was older than Yosef [as we know from Chumash, where Leah prayed for her 7th pregnancy not to result in a son since that would shame her sister Rachel]. Hence, according to any opinion, Dinah would have to have been a minimum of 8 at the time.
In any case, combining the two opinions would present a serious difficulty. If you will take the opinion that she was 3 (pending citation of a valid source for that) you will not be able to claim that Osnas was born of that union. Correct me if I am wrong.
As far as Tzipporah, I have no proof one way or another. But the account given lends itself to the assumption that she was not as old as Moshe (nearly 80). Aside from the way we are told about them as “daughters” indicating their youth, the fact no meforshim remark on her bearing children as miraculous indicates that it was ordinary (i.e. not an 80 year old woman). Beyond that, I will hark to Wolf who believes the burden of proof rests on you.
Just out of curiosity, what gave you the idea to randomly choose these two marriages as close in age? You don’t seem to have any proof, and there is also no obvious reason to think it was so. If you were looking for examples (other than the one I presented jokingly) you could have gone with the meforshim who say the shevotim married their own twins.