"image" is not defined in this scope

I am new to coding and need some help debugging…I am trying to classify a region in Peru using Sentinel 2. The error I am receiving is "’image’ is not defined in this scope." I believe my issues is on line 31 and the fact that I am working within a collection not an image…but I am still completely lost. Any tips?

var growth = ee.FeatureCollection('users/gtnatia/just_trees_training_2');
growth = growth.geometry();
Map.centerObject(growth);
Map.addLayer(growth, {color: 'red'}, 'growth');

//

var all_other = ee.FeatureCollection('users/gtnatia/all_other_training');
all_other = all_other.geometry();
Map.centerObject(all_other);
Map.addLayer(all_other, {color: 'black'}, 'all_other');


// Make a cloud-free Landsat 8 TOA composite (from raw imagery).
var sentinel2 = ee.ImageCollection('COPERNICUS/S2_SR')
                    .filterDate('2018-01-01', '2018-12-31')
                    .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 20))
                    .filterBounds(aoi);

// Use these bands for prediction.
var bands = ['B2', 'B3', 'B4', 'B5', 'B6', 'B7', 'B10', 'B11'];

//

var polygons = ee.FeatureCollection([
  ee.Feature(growth, {'class': 0}),
  ee.Feature(all_other, {'class': 1}),
]);

// Get the values for all pixels in each polygon in the training.
var training = image.sampleRegions({
  // Get the sample from the polygons FeatureCollection.
  collection: polygons,
  // Keep this list of properties from the polygons.
  properties: ['class'],
  // Set the scale to get Landsat pixels in the polygons.
  scale: 30
});

// Create an SVM classifier with custom parameters.
var classifier = ee.Classifier.libsvm({
  kernelType: 'RBF',
  gamma: 0.5,
  cost: 10
});

// Train the classifier.
var trained = classifier.train(training, 'class', bands);

// Classify the image.
var classified = image.classify(trained);

// Display the classification result and the input image.
Map.setCenter(-72.355,-13.880, 9);
Map.addLayer(image, {bands: ['B4', 'B3', 'B2'], max: 0.5, gamma: 2});
Map.addLayer(polygons, {}, 'training polygons');
Map.addLayer(classified,
             {min: 0, max: 1, palette: ['red', 'green']},
             'supervised_classification');