Data published yesterday by NHS Digital shows 137,629 patients were admitted in 2015-16, up from 119,168 in 2005-06.
The body said admissions across England have reached a record high, with an increase of 12.7m in 10 years.
At Portsmouth Hospitals NHS Trust, the mean age has also increased from 50 to 55.
Data shows the number of finished consultant episodes has grown from 140,001 to 166,404 in 10 years.
People aged over 75 account for 46,748 consultant episodes, up from 31,600 in 2005-06.
The increase is accounted for because of the closure of Royal Hospital Haslar in Gosport and changes to St Mary’s Hospital during the period.
Statistician at NHS Digital Jane Winter said: ‘The number of admissions to hospital has been rising steadily for over a decade now.
‘Admissions in 2015-16 were the highest on record, and over the past 10 years have risen at a faster rate than the population increase.
‘For example, the number of 65 to 69-year-olds has increased by 34 per cent in the past 10 years, with corresponding hospital admissions growing by 57 per cent.’
Nationally, patients aged 65 to 69 made up the single largest group of hospital admissions, when broken down into five-year age bands.
They account for some 1.3 million admissions in 2015-16, according to the NHS Digital figures.