Are they really going to have this big plot line of a mysterious hour-glass and tell us they don't have much time left, and then only do silly slice-of-life things? Why not just forgo all that crap then and just have them turn young for no particular reason? Because it seems like a weird distraction and not really tonally consistent.
Also, what happened to them wanting to travel and do things they didn't get to do when they were young? THEY'RE PLAYING CROQUET, THAT IS THE MOST OLD PERSON THING YOU CAN DO IDIOTS!