I have a 1979 Day Sailer II and LOVE it! I am a bit younger (44 yoa) than you, but my 71 year-old Dad comes with me often. I have found that the DS II is pretty stable, however...she IS a centerboard boat and MUST be sailed like one. Before my Dad sold his CAL 21, I used to sail singlehanded most of the time on windy Buzzards Bay near Cape Cod, the DS II handles those conditions pretty well, but I am careful. I added a tiller extension and that allows me to sit out on the side deck while sailing, putting my 200# (guess I need to lay off the sweets!) out there adds a lot of righting force, however it is not a problem sitting on the cockpit seats most of the time! The first VERY important tip is to ALWAYS keep the mainsheet in your hand! Use the camcleat to hold the tension, but keep the sheet in hand so that you can instantly release the sheet to spill the wind in a puff. Using that technique I have sailed my DS II for 13 seasons now without a capsize (and 7 seasons in a Widgeon before that!), I admit that I have had a couple of "close-calls", but other than a cockpit half full of water....I avoided going over! The DS II has a bailer that will drain out that water, slowly...but it WILL drain!
The other important tip is that like all of the small O'DAYs with a large mainsail and small jib, the DS II sails very well with just the main (raise the CB a bit to compensate). I often go out that way and it is more comfortable (and reduces my need to sit out on the deck!). The other big help was adding a set of reefpoints to the mainsail, that way I can reduce the sail area on a windy day and further reduce the heeling. The DS II comes from the factory with roller-reefing on the main, but it really doesn't work that well, especially since unless you have the optional roller-reefing claw.......you have no place to re-attach the mainsheet after rolling in a reef!
I am more than willing to answer any more DS II questions! Including supplying an expanded Owners Manual/Rigging guide.