Forget discount store bikes - period. Real bicycles are sold through real bicycle shops. If you are anywhere close to 4' 10" tall or more, you're ready to move into an adult sized bike with a small frame size. You never stated your height. Real bikes come in various frame sizes. Let's take a mountain bike for example. Click on the link below & look on the upper left side of the web page. Note where it states sizes: 12, 16, 18, 20. Those are frame sizes in inches. 12" frame for smaller riders all the way up to a 20" frame for those over 6' tall.
Google 'bicycle shop' and your zip code. That brings them all up in your area. Go see them all - or at least as many as possible. Tell the sales person where & how you will be riding. All streets, all off-road, a little of both...they can recommend the right bike at the right size for you.
Naturally these bikes will be more expensive than discount stores. You get what you pay for. Real bicycle shops do not sell toys. Toys 'R Us does not sell real bicycles.