Some people are too old to ride at 35, others will keep enjoying it even into their eighties.
I commuted occasionally in my thirties, but the opportunity to do so again didn't return until I was over fifty. I'll be 63 this year and I'm still enjoying it. I've averaged about 4,000 km/yr, but in the past 12 months I've ridden 5,200. I track my rides on Strava and average about 25-28 km/hr. The speed has been consistent for the 4 years I've been using Strava. I ride only on the road, mostly for the commute, but usually adding extra distance on my way to and from work.
My diet is pretty good, but not fanatically healthy. I don't smoke but I probably drink too much. Genetics was kind to me so I don't worry about my weight.
On the medical side, we all have our issues. I missed 10 weeks riding in early 2018 to have a colonectomy, but my surgeon credited my good health with a speedy recovery. I have worsening cervical disc issues that have required some handlebar adjustments but I refuse to give up my drop bars yet.
Having fun is the key. Cycling will be a positive influence no matter how old you are or how far or fast you ride. If you're not having fun, and you're doing it because you feel you must to stay fit, it's likely not going to help.