That is because the provided dates are outside the range of Timestamp.
pd.Timestamp.min
Timestamp('1677-09-21 00:12:43.145225')
pd.Timestamp.max
Timestamp('2262-04-11 23:47:16.854775807')
Details here
If we need the dates even out of range
Then we can convert them to period using below code
raw_data = {'Event': ['A','B','C','D', 'E'],
'dates': ['08-12-1600','26-09-1400', '04-11-1991','25-03-1991', '10-05-1991']}
df_1 = pd.DataFrame(raw_data, columns = ['Event', 'dates'])
def conv(x):
day,month,year = tuple(x.split('-'))
return pd.Period(year=int(year), month=int(month), day=int(day), freq="D")
df_1['dates'] = df_1.dates.apply(conv)
df_1
Output
Event dates
0 A 1600-12-08
1 B 1400-09-26
2 C 1991-11-04
3 D 1991-03-25
4 E 1991-05-10
If we can ignore dates outside range
df_1['dates'] = pd.to_datetime(df_1.dates, errors='coerce')
df_1
Output
Event dates
0 A NaT
1 B NaT
2 C 1991-04-11
3 D 1991-03-25
4 E 1991-10-05
Bonus Fact
Why timestamp can hold values for around 584 years 1677-2262?
Since timestamps provides nano second precision and is stored in 64-bit integer, hence it can store around 584 years with this nano second resolution in 64-bit int space.