One can point to many facets of Space: 1999
that have not
aged well. Examples in-universe:
- The bell-bottoms.
- The reliance on computer printouts.
- The black-and-white CRT's.
- Having to walk over to the composts.
The VFX haven't aged well either, as a general statement. In spots it still looks great, but too often the Moon globe looks exactly like a model, one can tell when the Eagles are turning on wires, due to the way they sway, laser effects are exaggerated, etc.
But I'll second that "not aging well" is ambiguous or could mean a variety of different things.