The Adolescent Stage in English Mastiffs: What Happens Between 6–18 Months

Understanding the “Teenage Phase” of Giant Breed Development

Estimated Reading Time: 15–18 Minutes
Last Updated: July 2026

Quick Answer

The adolescent stage in English Mastiffs typically occurs between 6 and 18 months of age and is often the most challenging period for owners. During this time, puppies may temporarily regress in training, test boundaries, become more independent, and show fluctuating energy levels.

This behavior is normal and reflects neurological, hormonal, and physical development—not a loss of training or intelligence.

At a Glance

Best For: Owners with puppies 6–18 months
Difficulty: Intermediate
Primary Focus: Managing adolescent behavior changes in giant breed dogs
Key Concept: Adolescence is a developmental phase, not a behavioral failure

Understanding the Adolescent Phase

The adolescent stage is the transition period between puppyhood and adulthood.

For English Mastiffs, this phase is particularly significant because:

• Physical growth continues rapidly

• Hormonal changes increase independence

• Emotional regulation is still developing

• Training consistency is being tested

Even well-trained puppies may appear to “forget” commands during this stage.

In reality, they are not forgetting—they are testing.

Why Adolescence Feels So Different

Many owners describe this stage as:

• “My puppy stopped listening”

• “They became stubborn overnight”

• “Training was going so well, then it fell apart”

This is a normal perception shift caused by development.

Three major changes are occurring at once:

1. Hormonal Changes

Increasing hormones influence confidence, curiosity, and independence.

2. Physical Growth

Rapid growth can temporarily affect coordination and focus.

3. Cognitive Development

The brain is reorganizing how it processes impulse control and decision-making.

Common Behavioral Changes During Adolescence

During this phase, English Mastiffs may:

• Test previously learned commands

• Pull more on leash despite prior training

• Become selectively responsive

• Increase chewing or destructive behavior

• Show bursts of energy followed by long rest periods

• Display increased guarding instincts

• Become more distracted outdoors

These changes are temporary but require consistency.

The “Regression Illusion”

One of the most frustrating aspects of adolescence is what appears to be regression.

A puppy that was:

• Calm at 4 months

• Responsive at 5 months

• Suddenly becomes inconsistent at 7–9 months

This is not true regression.

It is the brain prioritizing new developmental input over previously reinforced habits.

Consistency is not lost—it is being challenged.

MKA Pro Tip: If your English Mastiff suddenly seems to "forget" commands between 7 and 12 months, revisit the basics rather than assuming training has failed. Five minutes of focused obedience each day often produces better long-term results than occasional hour-long training sessions. Consistency almost always outperforms intensity during adolescence.

Why English Mastiffs Are Especially Affected

Giant breeds experience adolescence differently than smaller dogs due to:

• Slower full maturity timeline (up to 24 months)

• Increased body mass affecting coordination

• Longer dependency on structured guidance

• Delayed emotional maturity compared to physical size

This creates a gap where the dog looks adult but behaves juvenile.

What NOT to Do During Adolescence

Avoid common mistakes that worsen behavior:

• Assuming the dog is “being stubborn”

• Increasing punishment instead of structure

• Dropping training consistency because progress feels lost

• Allowing freedom too early due to size

• Inconsistent rules between family members

These responses often increase confusion and delay maturity.

What TO Do Instead

The adolescent phase responds best to structure, not intensity.

Effective approaches include:

• Reintroducing basic obedience consistently

• Short, focused training sessions

• Structured daily routine (feeding, walks, rest)

• Controlled environments for success

• Calm repetition of known commands

• Limiting overexcitement in uncontrolled settings

Think of this stage as reinforcement, not introduction.

The Importance of Routine

Routine becomes especially important during adolescence.

A stable structure helps regulate:

• Energy levels

• Emotional responses

• Training reliability

• Behavioral expectations

English Mastiffs thrive when life is predictable.

Unstructured freedom often leads to confusion, not confidence.

From Our Experience

At Mastiff Kennel of America, we find that adolescence is the stage where many owners underestimate the importance of consistency.

Puppies that received strong early foundation work (socialization, boundaries, routine) typically pass through adolescence with manageable challenges.

Puppies that were given inconsistent structure early often show more extreme testing behavior during this phase.

The difference is rarely the dog—it is the continuity of guidance.

Common Mistake

One of the most common mistakes owners make is assuming adolescence is the time to “relax training because the puppy already knows it.”

In reality, adolescence is when training must be most consistent.

This is when habits are either solidified or weakened.

Did You Know?

Many behavioral experts consider canine adolescence to be one of the most critical development windows because it directly influences adult temperament stability and long-term obedience reliability.

Myth vs. Fact

Myth: My puppy is becoming disobedient.

Fact: Your puppy is going through a normal developmental stage where impulse control and independence are still forming.

Related Articles

• Understanding Fear Periods in English Mastiffs

• Why Is My English Mastiff Puppy Biting Everything?

• Teething in English Mastiffs: What to Expect and How to Help

• Why Is My English Mastiff Puppy Sleeping So Much?

• Understanding English Mastiff Puppy Body Language

• The First 30 Days With Your English Mastiff Puppy

• Early Socialization: The First 8 Weeks That Shape Your English Mastiff for Life

Final Thoughts

The adolescent stage is often misunderstood as behavioral decline when it is actually a critical phase of development.

For English Mastiffs, this stage is where structure either becomes permanent or breaks down.

With consistent leadership, clear expectations, and calm repetition, most puppies emerge from adolescence into stable, reliable adult dogs.

At Mastiff Kennel of America, we view this phase not as a setback, but as the final shaping period before maturity—where everything learned earlier begins to settle into long-term behavior patterns.