Will an ear piercing get infected if you open it up after 35 years?

If by reopening it you mean re-piercing it, then yes, theres a chance that it'll get infected. If the piercing is healed over, go get it professionally repierced. Scar tissue can be a little tough to pierce through. Repiercing it yourself with non-sterile jewelry greatly increases the risk of infection. If it hasnt healed over, its fine because scar tissue has formed and you arent creating a new wound.