Not tested, but you probably want something like this.
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDate *currentDate = [NSDate date];
NSDateComponents *comps = [[NSDateComponents alloc] init];
[comps setYear:30];
NSDate *maxDate = [calendar dateByAddingComponents:comps toDate:currentDate options:0];
[comps setYear:-30];
NSDate *minDate = [calendar dateByAddingComponents:comps toDate:currentDate options:0];
[datePicker setMaximumDate:maxDate];
[datePicker setMinimumDate:minDate];
Update for Swift 4.1
let calendar = Calendar(identifier: .gregorian)
var comps = DateComponents()
comps.year = 30
let maxDate = calendar.date(byAdding: comps, to: Date())
comps.year = -30
let minDate = calendar.date(byAdding: comps, to: Date())
datePicker.maximumDate = maxDate
datePicker.minimumDate = minDate
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