Copper wiring can last up until 100 years++. The copper itself is not the issue but the cabble sheath. If u are using good quality cable with correct spec, it can easily last up until 70 years++. Should you rewiring your whole house?depend on budget and safety

If ur house is a 2 storeys house, it is more convenient to have 2 DB. Easily to troubleshoot and if got any issue, the wiring route should be more shorter hence cheaper

Ask wireman to do insulation test.
This will confirm ur  cable in good quality or failed.

If only have 1 DB, its time to create sub DB for kitchen & upstairs.
Aircnd cable with 4mmsq , 10mA for water heater etc.

Main DB @ GF then one sub DB @ 1F so you only need to korek one hole (single tree trunk between GF & 1F) rather than a huge hole for 20-40 wires returning to GF

It will involve rewiring of the first floor circuits (lights, sockets, and water heater) to point back to a sub DB box on the first floor (1F).

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A check is best to ascertain the feasibility; putting in a sub DB is recommended for high ceiling/larger houses so that you won't need a lot of redundant runs back to main DB at the GF.

But first and foremost I would do a check on the existing cables, sockets, water heater related to ascertain the health and whether the existing DB box and wiring is up to code.

This is because houses built >30 years ago don't necessarily follow current standards, ELCB was used and they were so insensitive that they're only good for fire protection (does not save lives), and due to old age the old ELCB/RCD failed to trip.

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If you're in Klang Valley/Selangor area, do PM me for further discussion.