Without a doubt a this point in your life you haven't a clue as to the reality of bike riding. You have great memories and like the idea; XX pounds and years ago. That means the least expensive and most logical place to start is inexpensive but not cheap. See if the reality matches what you think. If it does then move in. If it doesn't chalk it up to a past good memory season and move on.

I'd sure take a look at the local bike store, or stores. Not too worried about any "relationship" because neither of you know enough at this time to have one. What you want is something inexpensive to start with the idea that when you know what you want this bike goes to another good home and you get a shop bike.

I'd also not look down my nose at department store bikes. They are typically good value for beginners or neighborhood bikers, which right now is what you are. Remember this is a forum of bike enthusiasts who by and large are far enough into the sport to be more than a little finicky and their advice reflects that. Be sure to have the bike adjusted by the store if they have someone who is skilled enough, or take it to a shop to be adjusted so everything works correctly. Has the added advantage of seeing what their attitude toward you is going to be.

For a few hundred dollars you can get a good start and then make a decision when you have more facts. That is what I did and it worked just fine. Plus, it had the added advantage of seeing how the shops treated folks like me. Some, wouldn't even walk across the store to say "Hi". Others immediately tried to sell me the top line bike; they knew where their profits lay. One took a look at what I was riding, asked what I thought about it and what I thought I wanted and then did a good job of selling me an upgrade. Oh yes, the old bike? I sold it at a garage sale for more than I paid for it.