That's a good question.
I would say you would probably do well to start exploring your options now.
As you mentioned, premiums only go up with time and you can get a better idea now by looking at what other offers are available.
Also, it might be helpful when you sit down with your current life insurance company to have some other alternatives you have explored.
If the company you are with views you as a valuable client, they will do everything they can to keep your business and knowing ahead of time what other options are available might give you some room to work out a better deal for sticking with your current company.
It could also work in your favor the other way in that a competitor may offer you a better deal if you switch.