That's interesting that your high school gym is open to older people. Most of the time you see this in colleges where they have older people they work with, or Alumni or what ever. Seems odd in high school, but each place is different.
I would suggest scoping out a time where they aren't there. Not only that, when I used to see old people workout on campus, they NEVER used the same stuff I did.
So if you mean 60-80yr olds are in there, I doubt they are under the squat rack or doing DB presses and what not.
You may be a little off the path and thinking what they use, you need to use. Should be the opposite.
I've worked with the older population before, and we would focus on balance, and would use bands, medicine balls, thera balls, and many LIGHT DBs and use machines.
I doubt it is that bad. Not to mention, older adults usually like to exercise early in the morning most of the time from what I have seen. Usually how it is.
My first impression before you mentioned them, was I thought you may be intimidated by the other high school kids that use the gym. This happens quite a bit where someone wants to learn or get into weight lifting, but because football players and other guys are in there, they are too scared they will get laughed at. Then the either go pay for a gym or dont do it at all.
NEVER let any of those people intimidate you. I was the same way once. In fact the first time I lifted was in COLLEGE. I hadn't the slightest idea what I was doing, but had buddies to help me. Most of the time you can find a few friends who lift to get you going unless you are the odd kid out in school.
The point is, we all have to start somewhere. I was just guessing you might have had that problem. But since you mentioned older people, I guess its all good