HPL

I am so new to racing that I've not raced yet. I did "race" one time in what could be called a "criterium"; fairly informal, and unfortunately run by the military. 10 mile race of 2 laps, in 3rd place and catching the team pair ahead of me......and then out of nowhere, a garbage or dump truck, a big yellow thing anyways wiped me off the road into sugar sand; history. I always thought traffic was stopped, detoured, or was made to use a dedicated lane only during a road race; I learned the hard way after being tossed into an ambulance that day; figured if this happens in racing I may as well stick to the roads with traffic I AM EXPECTING. That was over 30 years ago, now I just want to turn and burn and see what I've got. At present I have nothing; I can't even maintain 20 mph for a half hour, but I can ride 20 miles plus averaging about 17 mph. I do not use low gears very often, not a spinner. I remember my average speed as being around 23 mph for one to two hour rides and I could sprint up to about 35 mph. My last "organized" (not a race, but everyone approached it that way except myself) ride was in November. I road a 69 Raleigh Sports 3spd for laughs , but found that I was keeping with the pack on my 50 lb. behemoth (we had a couple tandems riding also) while others (I'll call them "kids", no offense to the younger generations) were riding all the new fangled stuff as well as fixies (which I hate, sorry). I had no problem riding the bike for about 25 miles that day finishing with the main pack. I don't have anyone to ride with so that's out; can't use my work commute for training because I live 40 miles away and work at midnight and although I've done the ride before, the semi-truck traffic at night is rather dangerous, and after about a 2.5 hour ride and 9 hours on the feet working my body is not quite happy about return trip and it doesn't leave me much time at home. my normal rides are 20-25 miles and I don't do well in the Florida sun. Went out last Friday at noon and after one and a half hours I returned home drained from the 100 degree temp. My only quality ride time is early (cooler but extremely humid) or early eves/nights which aren't that much cooler until late (my sleep time with my present hours).
Anyways, 55 years old, 5'7" at 140 lbs, so not in too bad shape except for the cycling side of the issue. I would like to try, but I have no confidence riding close quarters around others; I like my space! Should I try at all, ride the tail and be happy I'm trying to compete, or just stay out of everyone's way and ride the trails in solitude? I don't like experiencing any sport/activity from the couch, but I don't want to ruin others experiences with my ineptitude.
I tried MTB and crashed 6 times in 3 miles so that is not an option I still have to work!), cyclocross means a new bike (can I convert an old road to cross? wrong geometry?).
It also appears that I'll need a new vocabulary.
I would be using an older steel bike 70's-80's as equipment. Does this automatically make me look like an idiot with all the new stuff out there? DT friction shifting is fine by me and so is a 6 speed; riding an 8,9,10,11 speed is just wasting sprockets on me unless I'm in the mountains, but no, Florida "flatlands" primarily.
I would not be embarrassed by finishing last, only if not finishing at all; I expect that there are 80 year olds who would blow me away so I'm being realistic.

I can handle the truth; no sugar coating!