The longest you have owned any gear?

Phillips CD-80. Bought it from a local 20 years ago, sold it once and then bought it back from a local audiophile. Original box, papers ,transport screws,etc. May use it as a transport when I get more room.

1984/1985 I purchased my first hi-end system:
Threshold SA-2s, Fet Ten line and phono stages, Sota Star Sapphire with an SME V, Cambridge CD player, McIntosh MR80, and Snell A III speakers. The CD was replaced some ten years ago with an Ayre which I still have in my current system.
The system sounded great up until October 2015 when I decided I wanted a change and went to tubes. My old gear is stored in the basement for my son who doesn't have the room at his current location.

My aiwa ad f770 cassette deck, since 1983 to present. It still works as good as day one, with a new set of  belts. Second I guess would be 2 of the many tuners I own. The marantz st6000 and the cambridge t500.

I still have my Acoustics Research Amplifier, bought new in 1969 (50 years?!).  In active use until it was peacefully retired into storage in 2012.

My Ariston RD11S TT. Bought new in 1977 for $280 w/o arm. Added an SME 3009 and a MicroAcoustics 2002 cartridge. Presently have a Grace 707 and Denon 103 on it, along with a Hiraoka SE-22 mat (bought new in '78 for $20 from Harvey Sound, NYC). The Ariston/SME was purchased from Audiocom in Old Greenwich, CT (best HiFi store in Fairfield County).

My listening room :-)

That would be my Pioneer Elite PD-65 CDP. I bought it around 1992-93. With all the reasonably priced DAC's available today, it now does duty as a transport. The thing is a tank.

I was a high end dealer back in the early 80s and sold Phiiips CD players. Kept a CD-80 for myself and had it modified by someone in Iowa, I think. I also was a dealer for "Speaker Art" by Bob Gross. I have a pair of his Odessy speakers. I have spent the last 20 years trying to find a CD player that is as good as the Phillips. I've tried it with external DACs but the one in it sounds better than anything I can afford. My latest effort to replace it is with an Oppo 105. The Oppo sounds good but is not as musical or detailed as the CD 80. I'm 78 years old so my hearing may not be up to the task but I have some good hearing aids and still enjoy my music. One unusual thing. I just purchased a Naim Supernait 3 amp and the remote for it will control the CD player. 
Would like to hear form anyone who has "Speaker Art" Speakers or a Phillips/Marantz CD 80. Terry

My Thorens TD-166 MKII turntable that I bought new in 1977 while in high school.  I had it refurbished in 2019.  I use it almost daily.

My Thorens TD166MkII, bought new in 1984 with a second arm wand. Now somewhat modified, but with original motor, arm, platter and plinth. It was a big purchase for me then, one year out of college, but I refused to re-buy my LPs in CD form and wanted a ’table that would last longer than my Technics belt drive TT. It certainly has lasted. It will probably outlive me.  Also, my Advent New Large Utility speakers, now in a secondary system.  My HS graduation present in 1978, refoamed in 2017(?) by Miilersound. Still sound pretty good.

Have had a Magnum Dynalab FT-101A FM tuner for 30 years and it has never failed once. Sent it back to MD for upgrading last year. Next oldest is a Bryston B60R Integrated Amp that has served me well for 20 years. It did require servicing at 19 years but, fortunately, it was within the 20-year warranty.

Spatial Coherence Preamplifier is definitely the oldest thing I own - a 1977 purchase.  Next up is a bunch of Amber 70 power amplifiers.   About the same time frame I purchased a pair of Shahinian Diapason speakers with four subwoofers. Pretty much everything else I own is much newer although my Conrad Johnson electronics have been around since 1997 or so.   

Still my TT. Purchased in 1983. Responded in 2017. 

My current gear:
Cary 303 CD player I have been owning since 2001.
Altec 604E speakers since 2005.
EMT 948 turntable since 2011.

ROWLAND 8T 12 years it is still a classic amp.

I've own my Acoustat Spectra 33 electrostatic speakers since 1988, 33 years. I use them for maybe a week or two every few years.

I still own and play from time to time my Yamaha NS1000. I bought them new in 1978 in Emporia KS. They still sound fantastic. In fact I just recently took them out of my system and re-installed my Tyler Acoustics Woodmere II. I switch back and forth once or twice a year just for fun.  

10 years with a Valve Audio Predator. Still own it but Esoteric separates have replaced it. I will set up a 2nd system with ATC SCM 7v3's.

Pioneer TX-9100 tuner. Since 1974. Haven't used it in years. Cannot bring myself to sell. Way too beautiful. Way too memorable. 

https://stereonomono.blogspot.com/2015/04/pioneer-tx-9100.html
And something tells me, if I ever do a little refresh and hook it up, it will put streaming to shame.

https://audiokarma.org/forums/index.php?threads/simply-unbelievable-tx-9100.55353/page-2

I'm definitely not going to win the "oldest in-use component" prize here lol. In my current main system: Tannoy Canterbury GR speakers, 5 years. Out of all the gear I still have that I might actually sincerely use again: my SOTA Star turntable (now upgraded to Nova V), 14 years. BUT I've at least been rocking Tannoys as my main speakers for 15 years; my love for them has been consistent and unwavering since my early speaker setup days :) And Koetsu isn't too far off that metric either; one of them has been my main source/cartridge for 11 year now. 

Luxman T2 tuner bought in 1972 still plays occasionally.

I still have my wonderful Epos M22's from 2005.  They have played great music and served me and my wife well.