If DE Capt. or a few months' upgrade is not a possibility, I'd be leaning toward SIC on a large jet that flies mostly international.
FYI, if you are 65 or over you are limited to how much international you can do if you are flying Part 135. Asia/Europe/PACOTS/NATS are out. Carib, CA and SA are still possible.
If it's Part 91 (Corporate/Private) age is not a factor.
When you go from 121 directly and get that Unicorn DEC Part 91 job, let us know so we can be envious.
Thrive hires retired 121 people. The CP is one.