Welcome! We both have this issue, same-aged LOs and a thread by this name! Too funny!
I think the reason PUPD is generally not advised at this age is because many LOs find it too stimulating which isn't what you are going for. Usually shh pat is recommended for extending naps for younger babies, but as I am having the same issue, I clearly don't have all the answers.
Sometimes something in the routine needs an adjustment, and sometimes there might be something else going on with your LO - illness, milestone/development, SA, etc. Have you read any of Tracy's books?
I'll send a couple links that might help you get started. If you post your routine in EASY format, someone could take a look at it. I am finding that my LO is giving less cues, just found her hands, and needs a bit more A time - I think these are all possible factors in our short naps.
Teaching Sleep to Newborns and Young InfantsSleep interviews with TracyThere's lots of other great info in the FAQs on the nap (and other) board(s), but these seem to be the ones I most often re-read. You can also find info on A times and A time increases which I also often refer to.
As I am posting about this same issue, I was reminded that LOs this age are often doing 1h20 A, some a little more. How long is your LO doing? Do you get any tired cues?