New to dirtbikes/motocross.

At 5'6" you can still ride an 80 for a little while. And if a $500 bike runs for a little while, that's all you can expect of it. But if you've never ridden before and wanted to try it out and see if you can learn it, $500 is a reasonably cheap price of admission. By the time you outgrow the bike, possibly by the end of this summer, you'll know whether you want to make a bigger investment in a newer bike.

Who is footing the bill ? If it is you and it is going to be it for awhile be prepared to be on it awhile. I was in your boat when I was a kid and I had to buy everything. So just make sure you check it well. Lucky though 2 strokes are easy and cheap to do a top end on.

You will need some help working on it. You probably don't have the tools to do a top end.

The work you will be doing on a routine, daily and weekly basis, like tightening spokes and cleaning air filters, changing oil, and so on, are easy to do with simple hand tools. But even that you will have an easier time with if somebody that really knows what they are doing shows you how.

You're at the upper limit of fitting on an 80 right now. Grow another two inches and you'll start feeling like it's a bit small. However, for learning, the smaller bike is actually not so bad.