I can't offer an opinion on the little guy, since it could be quite a few different things, so I would also recommend that you have him see his vet as soon as possible. It may be the beginnings of a cyst, or he could have an infection somewhere that is causing swelling in the nodes under his arm. If he's broken the skin somewhere, and an infection is starting, it could also be the beginnings of an abscess. If it is an abscess, it will eventually get sore and cause him pain, so it would be best to find out exactly what it is before it gets any larger and begins to cause him problems.
As far as your older beardie is concerned, because of his age and the way that it looks, my guess would be that it is some type of tumor, which may or may not be cancerous. It would also be a good idea to have him see his vet, although the vet may recommend that nothing be done even if it is a tumor, other than keeping him comfortable, simply because of his age. In a younger beardie, they would probably recommend that it be removed, but in a beardie his age, I doubt that surgery would be recommended, simply because the risk may be too great. However, if he is in good health otherwise, I could be wrong, and maybe it could be removed.
In any case, you need to find out exactly what it it, before a decision can be made as to what to do about it, and if it seems to be growing quickly, I would do it soon before it becomes too large and invasive to do anything about it!