Summit may only be a name, but they definitely had their own design, wherever they shopped it out to. Yugoslavia was a common source for that model.
You might have to look closely at it in person to find the year of manufacture on a very small nameplate. Looks similar to mine, which are of 1980's vintage, although mine doesn't have plastic knobs. Most likely plastic would be somewhat newer as it could be cheaper. My WAG.
Perhaps the main wearing item to check would be the forward, reverse and brake clutch packs. If the machine is regularly adjusted to keep these clutches at a nice 'snap in' feel, and enough brake drag to stop the spindle in a few seconds, then they shouldn't warp all to hell, and create nuisance dragging that could make the spindle sluggish to engage and release.
There is a cover on the back of the headstock that is opened to adjust these clutches. There is a dog pawl to retract and then a ring to adjust on each clutch pack. Should only ever need to adjust one hole or two. They are fiddly to adjust, as the adjustment of one of them can seem to affect the center neutral position, when the brake clutch becomes active. Don't overtighten. The machine spindle should be able to shift smoothly from forward to reverse without pausing at about 220 rpm. Handy for threading near a shoulder. Adjust one clutch too tight and you'll have to get really rammy to make the transition, and that's not the way to operate.