NEVER RELEGATED and over 100

Not that relegation is yet on the horizon, but there are a few Premier and Football League clubs looking over their shoulders and worrying about the next few months of results. In world history the following clubs have NEVER been relegated from and have therefore stayed in their country's top flight division for over 100 years: (there are clubs eg Sporting Lisbon who have survived the drop, but under 100 years), Aberdeen, Athletic Bilbao and few others.....

Glasgow Celtic was founded 1890 Duration in top flight by 2020, 130 years
and the same for these Northern Ireland clubs:
Cliftonville
Glentoran
Linfield all founded in 1890
THEN
Penarol of Uruguay 1900 120 years
Club Nacional de Football Uruguay 1901 119  years
Aberdeen 1905 115 years
Club Guarani of Paraguay 1906  114 years
Club Olimpia of Paraguay 1906  114 years
Inter Milan 1909  111 years
FK Austria-Wien (Vienna) 1911 109 years
SK Rapid Wien 1911 109 years
Upjest FC Hungary 1912 108 years
Club do Regatas Flamengo Brazil  1912 108 years
Boca Juniors Argentina 1913 107 years
Cerro Porteno Paraguay 1913 107 yrs
Santos 1916 106 yrs
Ajax 1917 103 yrs
*Arsenal 1919 101 yrs, see below
Curiously no clubs of any serious note seem to be founded in 1920 but these were in 1921 and stayed in the top flight:
Hamburger SV (till 2018), Standard Liege (99 years), Bohemian FC (99), Feyenoord (99).

The club Arsenal, as we know it now, was originally called Dial Square, named after its London location. It then became known as Royal Arsenal FC and in 1891 became the first London club to turn professional. At this time Tottenham Hotspur were still in the Southern League.
In 1893 the club became known as Woolwich Arsenal, playing in Division Two, coming 9th out of 15. The club joined the First Division in 1904 having worked its way up the Second Division, to be runners up behind Preston.

The club was relegated in 1912-13 season to Division Two, renaming as Arsenal.

In 1919, The Football League voted to promote The Arsenal, to the newly enlarged First Division instead of the local rivals Tottenham Hotspurs. That didn't go down too well in North London although Tottenham won promotion to Division One in 1919-20 winning the Second Division by 6 points and scoring over 100 goals, conceding only 32 in 42 games.