A Trial Investigating the Exposure of NN5401 in Young Adults and Elderly Subjects With Type 1 Diabetes

Inclusion Criteria: * Male or female aged 18-35 years (both inclusive) (young group) or at least 65 years (geriatric group) * Type 1 diabetes mellitus (as diagnosed clinically) for at least 12 months * Body mass index 18.0-28.0 kg/m\^2 (both inclusive) * HbA1c (glycosylated haemoglobin A1c) maximum 10.0% by central laboratory analysis Exclusion Criteria: * Subject who has donated any blood or plasma in the past month or more than 500 mL within 3 months prior to screening * Smoker (defined as a subject who is smoking more than 5 cigarettes or the equivalent per day) * Not able or willing to refrain from smoking and use of nicotine gum or transdermal nicotine patches during the inpatient period