That one definitely.
Dabbled in Shodokan Aikido a few years ago and started doing Krav Maga in the last few months. Thoroughly enjoying it but very aware of very much being in the foothills.
51 last month... it hurts.
Stick with it - I got my black belt in Aikido last year a few weeks before my 63rd birthday.
There are youngsters in the club who can run rings round me physically, but they don't have as much experience, low cunning or a killer attitude...