It's rare, but not unknown for some babies to drop to one nap as young as 7/8months old & some (like my niece) drop naps completely before 18months old.
Rather than look at age and textbook routine, look at how well your baby is coping. It may be a blip that improves in a week or so with some new skills learnt in the awake time, or it may be that with 12+ hours at night and a 2-hour nap in the day, it's enough for your baby to be a happy healthy child.
It might be worth moving the first nap to around 4+ hours from wake up time and see if you get one longer nap.
Just remember a baby who is happy tends to be doing what it right for them! no matter what the routines in books say.