Personally I think it would be a great idea to keep some money in bitcoin for retirement. By that age I think bitcoin could be worth many times what it is now. Keeping the other half in fiat would be advisable too but we all know money depreciated drastically especially when they keep printing more and more of it.
Yeah keeping some money in bitcoins is a great idea, as we never know what value its going to reach in the future, and rest of the money would be diversified and invest in gold, as gold can also be a good investment product in the future giving some good returns on the investment.