Question - Is there any way to accurately determine the age of a snake?

I bought my first BP at an expo this past weekend, and to be honest my head was spinning a little with excitement. I did ask how she was eating and what, and was told she was eating live fuzzy/hopper size very well, once a week. Well, I put on the scale last night and she only weighs 75g. She fits in my hand easily when coiled. Her thickest part is probably around an inch or a little over. I thought he said she had eaten good for the past 4 or 5 weeks, but that would put her at or over a month old, and that weight seems light for that age that is feeding well (from what I've read).

I got some frozen fuzzy mice today and will try her first feeding tonight.

My guess is one of two things... either the snake is only a month or so old, or it's older, but has maybe been underfed (as I've read some breaders do to keep cost down) and maybe he was just giving me a line of crap at the show in order to sell his snakes. Now that it's too late, I know it's good to ask for a clutch/hatch date and a feeding record on paper. I guess maybe a few months off from her actual age isn't a huge deal as long as she's healthy. I was planning on starting her on fuzzy f/t mice around every 5 or 6 days until she gets a little bigger.