Well, the universe is expanding at an accelerating rate. There's also a lot we don't quite know about the universe, including what it might look like from the "outside." I feel like the laws of physics that apply here on Earth or even elsewhere in the universe for particular objects aren't necessarily going to be the same for the universe as a whole. Also, the universe is probably not a bubble. It's often depicted more like a super weird cone or funnel that's expanding from its origin point, but I don't know if its shape can even truly be defined or hypothesized, since we can't observe it from the outside (if there is an "outside") and we don't know how things like dark matter or spacetime might affect the visual appearance of something as massive as the universe from the "outside".

We have to remember that, as far as we know, (and, frankly, even though we have learned/are learning a lot about the universe, we still really DON'T know a lot) the universe is infinite and there may or may not be something "outside" of it. Maybe there is, maybe ours is one universe in a multiverse, maybe there's literally nothing other than our universe (and whatever other realities/dimensions it might contain). It's just important to remember to be careful about absolute statements because the universe is so, so very complex, and calculating its age or its diameter isn't as simple as calculating the age/diameter of a bubble or even of the Earth or Milky Way.