There is no single age at which all pets become senior, because dogs age at different rates depending on their size and breed.

As a general guide:

One key principle: one year in a senior pet’s life can equal several human years. Changes in their health can progress quickly. This is precisely why the AAHA recommends twice-yearly wellness examinations for senior pets — not because something is necessarily wrong, but because the window for catching conditions before they become serious is shorter.

The Most Common Health Conditions in Senior Pets

Osteoarthritis (Joint Disease)

Arthritis is one of the most widespread and most underdiagnosed conditions in older pets. Research suggests that over 60% of dogs experience some degree of arthritis, and the condition is similarly common in older cats. Yet because pets instinctively hide pain and adapt their movement gradually over time, many owners do not recognise it until it is well advanced.

Signs of arthritis in dogs: Reluctance to jump, climb stairs, or rise from rest; stiffness in the mornings that improves as the pet warms up; reduced activity and play; lagging on walks; occasionally licking or chewing at painful joints.

Signs of arthritis in cats: Reduced jumping height or avoidance of furniture they previously used effortlessly; reluctance to use a litter box with high sides; grooming changes (less able to reach certain areas, or overgrooming painful joints); reduced activity and interaction.

Modern veterinary management of osteoarthritis includes several well-evidenced approaches: appropriate pain medication, anti-inflammatory therapy, weight management (reducing the load on painful joints), therapeutic nutrition including omega-3 fatty acids (which have demonstrated analgesic effects in peer-reviewed research), and in some cases, physiotherapy and mobility aids.

Important: Never give your pet human pain medications for arthritis. Ibuprofen, paracetamol, and naproxen are toxic to dogs and cats. Vet-prescribed pain management is both safer and more effective.

Chronic Kidney Disease (CKD)

Kidney disease is one of the most significant health concerns in older cats, and is also common in senior dogs. Data from large veterinary laboratory studies shows that CKD is detectable in over 40% of cats aged 5 to 15, and in over 80% of cats aged 15 and above.

The challenge with kidney disease is that it is clinically silent in its early stages. By the time a pet shows obvious symptoms — increased thirst and urination, weight loss, vomiting, reduced appetite — significant kidney function has already been lost. This is the core reason why routine blood and urine testing in senior pets is so valuable: it can detect kidney disease when it is early, before symptoms appear, at a stage when dietary and medical management can meaningfully slow progression and extend quality of life.

Early detection through twice-yearly wellness bloodwork is one of the most important things you can do for an older cat especially.

Cognitive Dysfunction Syndrome (CDS)

Cognitive dysfunction syndrome is the veterinary equivalent of dementia in humans. It is a recognised neurological condition associated with age-related changes in the brain, and it is more common than most pet owners realise.

The clinical signs in dogs are captured under the acronym DISHAA: Disorientation, altered Interactions (with people and other pets), changes in Sleep-wake cycles, loss of House training, altered Activity levels, and increased Anxiety. A dog who begins waking at night, pacing, seeming confused in familiar environments, or staring at walls may be showing signs of CDS rather than simply being “old and odd.”

In cats, cognitive dysfunction tends to present differently — cats often increase vocalisation (particularly at night), become clingier or more anxious, and may show confusion in familiar environments.

CDS is a diagnosis of exclusion — meaning other medical causes must be ruled out first. Once diagnosed, it can often be managed with environmental enrichment, mental stimulation, specific nutritional support, and in some cases, medication.

Dental Disease

Senior pets accumulate years of dental disease progression. By the time a dog or cat reaches senior age without consistent dental care, many will have moderate to advanced periodontal disease causing chronic pain and systemic bacterial exposure. We assess dental health at every senior wellness visit at Diamond Claw, and professional dental cleaning remains as important — often more so — in older pets as in younger ones.

Endocrine Diseases

Hypothyroidism is common in older dogs, causing weight gain, lethargy, skin changes, and hair loss. Hyperthyroidismis one of the most common diseases in older cats, causing weight loss despite increased appetite, increased thirst and urination, restlessness, and a rapid heart rate. Diabetes mellitus affects both species and becomes more common with age, particularly in obese or previously obese pets.

All of these conditions are detectable through routine blood testing and manageable with appropriate treatment. Left undetected, they significantly affect quality of life.