Hello
I have recently made a 2 block tall crop. Problem: The upper block of the block doesn't seem to update with age, always staying at the first stage.                                            Here's the first stage of the plant:

Here is the last stage:

Here is the code I used for the crop:

public class AncientFruitBlock extends CropsBlock {
       
 
 
    public static final IntegerProperty AGE = BlockStateProperties.AGE_0_5;
    public static final EnumProperty<DoubleBlockHalf> HALF = BlockStateProperties.DOUBLE_BLOCK_HALF;
    private static final VoxelShape[] SHAPE_BY_AGE = new VoxelShape[]{
            Block.makeCuboidShape(0.0D, 0.0D, 0.0D, 16.0D, 3.0D, 16.0D),
            Block.makeCuboidShape(0.0D, 0.0D, 0.0D, 16.0D, 6.0D, 16.0D),
            Block.makeCuboidShape(0.0D, 0.0D, 0.0D, 16.0D, 11.0D, 16.0D),
            Block.makeCuboidShape(0.0D, 0.0D, 0.0D, 16.0D, 16.0D, 16.0D),
            Block.makeCuboidShape(0.0D, 0.0D, 0.0D, 16.0D, 16.0D, 16.0D),
            Block.makeCuboidShape(0.0D, 0.0D, 0.0D, 16.0D, 16.0D, 16.0D)};
            
            
    
    public AncientFruitBlock(Properties builder) {
        super(builder);   
        this.setDefaultState(this.stateContainer.getBaseState().with(HALF, DoubleBlockHalf.LOWER));
    }
    
    public BlockState updatePostPlacement(BlockState stateIn, Direction facing, BlockState facingState, IWorld worldIn, BlockPos currentPos, BlockPos facingPos) {
        DoubleBlockHalf doubleblockhalf = stateIn.get(HALF);
        if (facing.getAxis() != Direction.Axis.Y || doubleblockhalf == DoubleBlockHalf.LOWER != (facing == Direction.UP) || facingState.isIn(this) && facingState.get(HALF) != doubleblockhalf) {
           return doubleblockhalf == DoubleBlockHalf.LOWER && facing == Direction.DOWN && !stateIn.isValidPosition(worldIn, currentPos) ? Blocks.AIR.getDefaultState() : super.updatePostPlacement(stateIn, facing, facingState, worldIn, currentPos, facingPos);
        } else {
           return Blocks.AIR.getDefaultState();
        }
     }
    
    @Nullable
    public BlockState getStateForPlacement(BlockItemUseContext context) {
       BlockPos blockpos = context.getPos();
       return blockpos.getY() < 255 && context.getWorld().getBlockState(blockpos.up()).isReplaceable(context) ? super.getStateForPlacement(context) : null;
    }
    
    public void onBlockPlacedBy(World worldIn, BlockPos pos, BlockState state, LivingEntity placer, ItemStack stack) {
        worldIn.setBlockState(pos.up(), this.getDefaultState().with(HALF, DoubleBlockHalf.UPPER), 3);
     }
 
     public boolean isValidPosition(BlockState state, IWorldReader worldIn, BlockPos pos) {
        if (state.get(HALF) != DoubleBlockHalf.UPPER) {
           return super.isValidPosition(state, worldIn, pos);
        } else {
           BlockState blockstate = worldIn.getBlockState(pos.down());
           if (state.getBlock() != this) return super.isValidPosition(state, worldIn, pos); //Forge: This function is called during world gen and placement, before this block is set, so if we are not 'here' then assume it's the pre-check.
           return blockstate.isIn(this) && blockstate.get(HALF) == DoubleBlockHalf.LOWER;
        }
     }
 
     public void placeAt(IWorld worldIn, BlockPos pos, int flags) {
        worldIn.setBlockState(pos, this.getDefaultState().with(HALF, DoubleBlockHalf.LOWER), flags);
        worldIn.setBlockState(pos.up(), this.getDefaultState().with(HALF, DoubleBlockHalf.UPPER), flags);
     }
 
     public void onBlockHarvested(World worldIn, BlockPos pos, BlockState state, PlayerEntity player) {
        if (!worldIn.isRemote) {
           if (player.isCreative()) {
              removeBottomHalf(worldIn, pos, state, player);
           } else {
              spawnDrops(state, worldIn, pos, (TileEntity)null, player, player.getHeldItemMainhand());
           }
        }
 
        super.onBlockHarvested(worldIn, pos, state, player);
     }
 
     public void harvestBlock(World worldIn, PlayerEntity player, BlockPos pos, BlockState state, @Nullable TileEntity te, ItemStack stack) {
        super.harvestBlock(worldIn, player, pos, Blocks.AIR.getDefaultState(), te, stack);
     }
 
     protected static void removeBottomHalf(World world, BlockPos pos, BlockState state, PlayerEntity player) {
        DoubleBlockHalf doubleblockhalf = state.get(HALF);
        if (doubleblockhalf == DoubleBlockHalf.UPPER) {
           BlockPos blockpos = pos.down();
           BlockState blockstate = world.getBlockState(blockpos);
           if (blockstate.getBlock() == state.getBlock() && blockstate.get(HALF) == DoubleBlockHalf.LOWER) {
              world.setBlockState(blockpos, Blocks.AIR.getDefaultState(), 35);
              world.playEvent(player, 2001, blockpos, Block.getStateId(blockstate));
           }
        }
 
     }
     
     @Override
     protected void fillStateContainer(StateContainer.Builder<Block, BlockState> builder) {
        builder.add(HALF);
        builder.add(AGE);
     }
     
     public IntegerProperty getAgeProperty() {
         return AGE;
      }
 
    @Override
    protected IItemProvider getSeedsItem() {
        return ItemInit.ANCIENT_SEED.get();
    }
    
    @Override
    public int getMaxAge() {
        return 5;
     }
 
    @Override
    public VoxelShape getShape(BlockState state, IBlockReader worldIn, BlockPos pos, ISelectionContext context) {
        return SHAPE_BY_AGE[state.get(this.getAgeProperty())];
    }
 }

What do I have to do to fix this? Thanks in advance.

I will recommend only place the top block when the bottom one is fully grown.

Could you give me a rough explanation on how to do this? It would be really helpful.