Ideal or not it will depend on your plan, if the plan to start buying Bitcoin is only a few years before retirement then it is not ideal because you can be in a hurry to sell it immediately because of retirement needs even though the return is not yet large, also the short period of storing Bitcoin does not provide much experience or view of how the Bitcoin market works so you can be hit by panic when you see a volatile market, so the sooner you start your plan the greater the return that can be given because you already understand the Bitcoin market.