No. It's the average of your last 10 transactions, so in theory it should average out even through pay cycles, but I find it doesn't work perfectly when you're paid monthly (Americans are paid fortnightly) as it will cycle up to a max of about 30 just before payday and then crash down into single digits again about a week later. For the first few months I used a spreadsheet to track it throughout the month to see the average grow/make pretty graphs. The novelty of that wore off and I mostly ignore AOM now.
They say it is like this (remember $1 bills are a thing) imagine you got paid as a stack of dollar bills. You put them into something like a napkin dispenser and take money from the bottom of the pile each time you spend. When you get more money, it goes into the top. Your age of money is the amount of time each dollar spends in the dispenser before it is spent.
Or another analogy is that each pay packet is a physical envelope so it's the amount of time you can still be spending out of one single pay packet before having to open the next one.
So if you're like most European people and get paid monthly with most of your monthly bills set to go out on DD shortly after payday then your money you put in when you last got paid (or started YNAB) will start to run out just as loads of big transactions take place, and this will cause your age of money to drop because you only just got the "pile" of money you're currently spending from. But over time you'll see the low point get higher and higher.