You are not too old. I am 40, started cycling last year, did 1 x 100k last year, a couple of 100k rides this year, plus lots of social rides and a reliability ride. Did 2 x 200's, what made it happen for me was the support of others on this forum, the likes of Fidgetbuzz, ChrisS, Maladict. Charlotte, Liz, Teethgrinder and Andrij.
Sort out your nutrition and off bike time, get out and just do it and be proud of your achievements. I never thought I would ride a 200 but there you go. Next step is to do a couple more 200's and then a 300.
Never say never.
Enjoy.