Four ages means four different ideas of height
A kitten, two middle-aged cats and a senior do not want the same vertical world. The youngster wants altitude and launch points; the middle pair want comfortable lookout shelves; the senior, whose joints may make big jumps a negotiation, wants modest height reached by steps or a ramp — and still deserves a raised place of her own rather than exile to the floor. Designing one spectacular tower serves only the strongest climber, who will then own it and guard it. The working answer is a connected network of routes at staggered heights, so each cat can be above the floor on terms her body and confidence allow.
A low line for the senior, built like furniture not apparatus
Give the oldest cat a route of wide, shallow steps: a sturdy low bookcase, then a chest, then a padded window ledge at sitting height, linked by surfaces she can walk rather than jump between. A carpeted ramp up to the first level removes the hardest leap entirely. This low line should pass through the warm, social rooms rather than ending in a spare corner, because senior cats usually want company at their altitude, not isolation. Keep her favourite blanket on the final ledge and make sure the youngster's games do not route through it at speed — a quiet line stays quiet by design, not by hoping.
The middle circuit and the high line
For the middle-aged pair, wall shelves or the tops of tall furniture at door height make a satisfying circuit between rooms, with at least two perches of equal quality so they are not competing for a single sunny spot. The youngster's high line can share the same wall: continue one shelf run upward to a top perch near the ceiling, reached by a tall post. Crucially, every level needs two ways off — a route that dead-ends at a popular perch manufactures confrontations when the cat coming up meets the cat coming down with nowhere to pass. Loops, not ladders, are what keep a multi-cat height system peaceful.
Duplicating the prizes and watching the traffic
Whatever the cats value most — the window view of the street, the shelf above the radiator, the sun patch at midday — provide it twice, at different heights or on opposite walls. Duplication is the cheapest peace-keeping in a four-cat house. Then watch the traffic for a fortnight: a perch nobody uses is usually a perch approached past another cat's resting place, and moving its access step a short distance fixes what looks like pickiness. Note which cat claims which level at which hour; in a mixed-age group those patterns shift as the senior slows and the kitten grows, and small rearrangements each season keep the network matched to the cats you actually have.
A standing check that keeps four routes safe at once
Four cats using three interlocking routes means more fixings, more worn pads and more chances for one loose shelf to go unnoticed in a busy house. A regular circuit check — tug the shelves, inspect the senior's ramp surface, wash the most-used pads — protects the oldest and youngest cats most, since they are least able to recover from a collapsing landing. Scheduling that check on KinsLe Care Teams, with the duty marked complete and timestamped each time, keeps the whole vertical network inspected as one habit rather than four separate things to remember.