Give it an address inside the tank
A community tank is a busy place, and an elderly guppy that once thrived in the middle of it increasingly needs an address of its own: a corner thick with fine, feathery planting where the current is low, the light is softened, and faster fish rarely bother to push in. Build that refuge at the level where the senior already rests, rather than at the surface or the gravel simply because space is free there.
Keep the refuge permanent. Guppies learn the tank by landmarks more than keepers realise, and a frail fish that returns nightly to the same plant tangle should not find it pruned into a different shape every maintenance day. Trim around it if you must, but leave the senior's own patch recognisably itself.
Take the pressure off at the edges
Most home adjustments for an old guppy are really adjustments to its neighbours. Persistent chasers, fin-nippers, and males that will not leave a worn female alone turn ageing into harassment, so separate the offender or the senior before you change anything else. A small fish being harried spends its remaining strength on escape, and no feeding plan compensates for that.
Current belongs on the same list. A filter outflow that younger guppies ride for fun can pin a senior against the glass or exhaust it on the swim back to shelter. Deflect the stream along the back wall so the refuge corner stays nearly still while the open water keeps its movement for the rest of the group.
Feed the edge, not the scrum
Scatter a little fine food so some of it drifts into the refuge rather than concentrating the whole meal at the centre of the surface. The senior can then feed from the edge of cover, taking small pieces without entering the jostle, and you can see from its posture whether it is actually eating or merely present. Add a deliberate second offering at that corner if the group strips the water column before anything reaches it.
Water steadiness is the quiet adjustment underneath all the others. Small, matched water changes, a heater and filter checked rather than assumed, and no sudden additions of new fish all protect a senior whose reserves for coping with change are nearly spent. New arrivals in particular can wait; the old fish's stability is worth more than the group's novelty.
Know when the community tank is the problem
If the guppy still loses condition in its refuge, or spends the day hiding rather than resting openly in the plants, move it gently to a small, cycled, calm tank of its own, taking some of its refuge planting with it. For a fish near the end of a short life, a peaceful single room with food delivered to its mouth is not isolation; it is comfort care.
Keep the move low-stress: same water where possible, dim light, no chasing with the net. A senior guppy cornered repeatedly around the tank can be injured by the rescue itself.
Those small arrangements are easy for a second keeper to miss entirely, so KinsLe logs them in its Pet Passport where the guppy's refuge, feeding edge, and separation plan are written down rather than left to memory.