Just have fun. Everyone who has posted here has given some really good information. There is no "right" speed. As someone who tends to judge herself by comparing herself to others, I can say it just isn't healthy, and won't make you happy.

I've been riding off & on since I was a kid, so I really can't say where I was as a newbie. If I wasn't riding, I was swimming or skiing (i.e., when I'd get on my bike, I'd still be faster than if I'd been doing nothing). I was faster in my 20s, when I got my first computer. 20-some years later, yeah, I'm slower at everything. I'm also riding farther on my longest rides, though.

Right now, on my mtb, which I ride anywhere from 0-3 times per week in the summer, I'll average maybe 6-8 on singletrack trails. Faster on 2-track and dirt roads. On my road bike, which I ride by far the most, I'll start the season at around 13-15, and usually end up 16-18 by September (by October the weather is cruddy for biking, and I'm bored & ready to ski anyway, and enter my Fall Doldrum period until the snow flies). Hills vs flats, wind vs no wind - that will all make a huge difference. Yesterday (my second ride of the season), I did 23 miles at some speed, with a the wind gusting to 30 - I knew it was silly to look, because it just didn't matter. I had fun!

Example: Yesterday - I'm guessing 14-ish (that gusty wind was at our backs for about 10 miles). Last summer ONE TIME, on a point-to-point ride with big rolling hills and a 30mph tailwind, 19.5 (my most-fun ride EVER). On a typical solo 100-miler, 14-14.5 average, pretty darn consistently.