My clock started ticking its butt off around 15 years of age... To the point that I would poke holes in my boyfriends condoms... Stupid thing to do I know but I jut new that my only real ambition in life was to be a mummy.... My Aunty even told me when I was in primary school and the "what do you want to be when you grow up" question was asked, my response was always - a mummy.
My view is, if you are in a stable loving relationship and are financially able to give your baby everything it needs, why wait? I don't think there is an "acceptable age" as such, and it changes from person to person. I know plenty of 30+ year olds who aren't ready yet, and plenty of early 20 year olds who ate actively planning there families.
Do what is right for you xxx