In a Long Runnign Rut??

[Gybe99]

I think I already know the answers, but wanted to get some feedback regardless.
I have been working out regularly, 3-4 days/week (early morning) for the last 23 years.
(I am 55 yrs old). 6'0" 193 lbs, have pretty good definition.
Work out so I can play on the weekends, sailing, windsurfing, hunting, fishing etc.
I look forward to going each morning and feel good about it afterwards.
Work out consists of 15 min on stationary bike, 100 Push ups, 100 sit ups
30 minutes of weights concentrating on 1 muscle group each day.
My question is, I have tweeked the lift routines over the years but for the most part have done the same all this time. I work up a good sweat every day, and have increased weight where possible, sets and weights to failure, but wonder if I am missing out by not mixing it up to confuse my body more.
I do the same because I can basically do it in my sleep, and know my limits minimizing chance of injury.
Comments welcomed.
Thanks