The day will come. Your brand new, off-the-rack wetsuit will one day just not keep you that warm anymore. It's time to buy a new one. Don't feel bad, you got a good 4-5 years of diving out of it; the investment has been well worth it. Besides, a new wetsuit won't set you back that much.
Just one thing remains: what do you do with the old wetsuit? Structurally it's still in decent shape, so it's a shame to throw it away. The good news is there's a reason to hold on to it. Keep the old wetsuit, and use it for situations where it's warm and the poor insulation won't make a difference. Things like training in a chlorinated pool or shore diving in very warm water are perfect.
There are two benefits from keeping an old wetsuit in the closet:
- It extends the life of your new wetsuit. By not using your new wetsuit in the pool, you save it from some harsh chemicals that will age it faster. Ditto for the wear and tear that comes any time you wear a wetsuit.
- It extends the life of your old wetsuit. Finding new uses for old things makes you feel good. You're keeping your neoprene knickers out of a landfill just a little bit longer.
Eventually it will get so old that it's not even appropriate for a swimming pool. By this point you should've gotten a long life out of the wetsuit, so you can throw it away with peace of mind. You may even be due for yet another new wetsuit, so you can continue this cycle indefinitely.