All is not lost, old timer. (I'm going on 55, BTW.) Proper exercise sequencing--ie, training smarter--can go a long way toward allowing you to work your muscles hard. The following is adopted from comments I made on the thread Eyedentist, how do you train?:
My thought process regarding workout programming changed dramatically after I did a 12-week program with John Meadows. He made me realize that a joint/tendon-friendly workout scheme is actually the opposite of the 'heavy compound movement first, isolation finisher last' approach I had followed for so long. Here is the blueprint I follow for each muscle group now:
1) The purpose of the first exercise is to begin getting blood into the muscle without putting undo stress on the tendons and joints. To do this, an isolation exercise is employed, light loads are used, and the ROM is limited to the final third (ie, approaching the fully contracted position) portion of the movement. The stretched position is avoided at all costs.
2) The next exercise(s) is/are the 'main course.' It is the only portion of the workout that feels heavy (reps will be in the 8-12 range). It is also the exercise on which I will use intensification techniques (drop sets, rest/pause, etc). The ROM will be the middle third of the movement; the stretch position is (still) avoided to minimize the risk of injury, and the lockout position is avoided to keep continuous tension on the muscle.
3) The purpose of the last exercise is twofold. First, it serves to drive as much blood as possible into the muscle; second, the now-fully-warmed-up muscle can (and should) be safely stretched by working throughout its full ROM.
This is how such programming can be applied to Triceps work:
1) Activation/warm-up movement: Occluded rope pushouts
--ROM: The contracted fifth. I use a very light weight, and pull the rope handles down and OUT (this is key!) as hard as I can. My thought is to pull the rope hard enough to literally render it straight (ie, parallel to the floor). I hold this extreme-contracted position for a 4-count, then 'break' the peak contraction, slowly lower the weight stack a few inches, then it's right back to the max contracted position for another 4-count. I can't emphasize enough just how short the ROM is--my hands NEVER get close to one another, and other than the first and last reps, the movement has no vertical (ie, up and down) component. (This is why I call them rope pushOUTS, not pushDOWNS.) Done correctly, these are brutal, and the pump is insane. (Credit Meadows for this one.)
--3 sets, 15-30 sec rest, ramping the weight
--Reps: 15-25; within 2-3 reps of failure
2) Hypertrophy movement: Conventional cable pushdowns
--ROM = middle 3/5s.
--3-4 sets, 2-3 min rest, reverse-pyramid style
--Reps: 8-12, reverse-pyramid style. Every set is within 1 rep of failure, and last set employs intensification technique(s)
3) Stretching movement: DB supine stretchers
--ROM : The stretched half. Basically, these are skullcrushers done with DBs (one in each hand, hands in the 'neutral' position), but with my head hanging off the end of the bench. I reach 'out and back' with the DBs (my upper arms are almost parallel to the floor) to put the triceps on-stretch. When I bend at the elbow, the DBs come back almost under my head.
--2-3 sets, 30-60 sec rest; weight changes by feel (ie, can go up or down depending on how the stretch feels)
--Reps: 15-25; within 1-2 reps of failure