Having a Bitcoin investment for 4 years is okay but you should start when the bear run comes. That will help you to buy Bitcoin at a lower price and keep buying using DCA methods. That also helps you to accumulate more Bitcoin than you started with at this time because the price has already increased. But if you want to start now, that will not be a problem...
This is the problem of newcomers who were afraid to buy bitcoin when its price was low, but now, after the price has updated ATH several times. So perhaps the best solution would be to wait for the price to decrease in order to proceed with DCA.