Minimum and maximum date in UIDatePicker

Try this:

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDate *currentDate = [NSDate date];
NSDateComponents *comps = [[NSDateComponents alloc] init];
[comps setYear:-18];
NSDate *minDate = [gregorian dateByAddingComponents:comps toDate:currentDate  options:0];
[comps setYear:-150];
NSDate *maxDate = [gregorian dateByAddingComponents:comps toDate:currentDate  options:0];
[comps release];

self.datePicker.minimumDate = minDate;
self.datePicker.maximumDate = maxDate;

It may be easily translated to Swift 4.2:

    let calendar = Calendar(identifier: .gregorian)

    let currentDate = Date()
    var components = DateComponents()
    components.calendar = calendar

    components.year = -18
    components.month = 12
    let maxDate = calendar.date(byAdding: components, to: currentDate)!

    components.year = -150
    let minDate = calendar.date(byAdding: components, to: currentDate)!

    picker.minimumDate = minDate
    picker.maximumDate = maxDate