battery replacement

Yes it can be normal. There is no real set rules or time frames for how long a battery will last since there are a lot of variables which affect the health of a Lithium-ion Battery. Generally speaking the majority of our organization's Apple laptops have batteries that typically last 3 to 5 years with some lasting even longer (some fail much sooner too).

The "Replace Now" condition just means that the battery probably only powers the laptop for an extremely short period of time. If you short runtime when using the battery doesn't bother you, then you can wait to replace the battery. However, you want to make sure that you don't wait so long that an official Apple battery repair is no longer available. Apple typically supports the hardware for about five years followed by a two year period where the Mac is considered "Vintage" and repairs can only be performed if the necessary part is still available (mail-in repairs may not be possible for "Vintage" products). You definitely want to have an official Apple battery since the quality of third party Lithium-ion batteries is extremely poor even when purchased from a respectable vendor.