I'm a 58 yo male, 4th Dan taekwondo, training for about 17 years, flexibility not the best, but for the last 18 months, I've been really putting in the training, weights, core work, stretching etc, I use a rope and and old white belt, slung over a rafter to try to improve my front stretch and side kick stretch, is this method ok to use? Using the pulley system, I can get my leg up over head high, but when doing it at a standing start, have trouble holding it there. I also do side leg raises and core work to try to strength my side kicks. Love to hear your advice.
I'm no doctor and if you want medical advice on the safety of stretching with a pulley you're asking in the wrong place, but it seems to me that as long as you're not feeling burning pain from excessive stretching, and in your stretching position you have enough control to ease back on the stretch if that were to start, all's good. Because when using a pulley you're standing in pretty much the extended kicking position, you're likely to be stretching pretty much all the muscles you really need stretched. Still, compared to stretching on the floor, it may be harder to introduce controlled PNF-style contractions and relax in a controlled fashion into a deeper stretch, so I'd suggest some combination. You might want to supplement the pulley stretches with other suggestions from this thread: Good exercises for higher side kicks?
As for "have trouble holding it there" - I know that's popular with tkd stylists but personally think it's over-rated from a fighting skills perspective, though some of the ITF hyungs require it (I didn't study WTF patterns much). A relaxed ability to reach those heights comfortably dynamically is important though, and the former only helps the latter. Anyway, you'll need to spend enough time in the stretched position to inhibit almost all the contraction, and also work on leg raises at increasing heights - you might want to do that with ankle weights, lifting the pulley to say 5-10 cm less than you can lift to, then lifting that extra distance for a few seconds, gradually increasing the time then eventually upping the height and repeating.
As for "strength side kicks" - if you mean kicking harder - IMHO hip rotation, technique and timing are significantly more important than muscle strength or flexibility. A lot of getting your leg up in the air comes from the rocking motion of the hips, good knee motion, good footwork. I made an instructional video on what I consider key fundamentals and concepts many years ago - but crappy spur of the moment thing, and depending on your TKD style (the post-WWII karate-derived style, modern WTF and ITF are all vastly different) you might well hate it, or know it all already, or even know better in general, or have something that just suits you or your sparring/fighting tactics better for whatever reasons, but for whatever it's worth: http://www.youtube.com/watch?v=uTtyTOLqnoc
Separately - for front kicks, I always found it great to sit on the kind of bench used for bench presses at the gym - just something maybe 1m+ long and 30/40cm wide, with your heel just over one end and the ball dangling relaxed rather than pulled back towards your hips (i.e. isolating the hamstring without simultaneously stretching the calf), the other leg out at 90 degrees, knee bent 90 degrees and foot on the ground, and to reach under the bench to pull your chest down over the leg, keeping the back straight. You get a lot of good leverage that way.
I use it occasionally as a replacement for a partner when attempting PNF stretching, which is how pulleys should be used. It's a bit awkward for me, and unless you have several pulleys located in different places (essentially, high and low, allowing for adductor and abductor stretching), you're not really getting the best benefit.
However, some people use them in a similar fashion that the stretch machines that Chuck Norris used to peddle. These, I've discovered, are dangerous because when you feel pain, it's difficult to release quickly, and the damage is done. With pulleys, pain can be lessened almost immediately, so it's moderately better than the machine. So as long as you are not pulling and locking (by wrapping one end of the rope around something), you should be fine.
One other caveat: be sure to use them in an active manner - PNF, actually. As you pull the rope and open (or close) the stretch, you need to fight against that exercise: that is the PNF exercise. If all you do it sit there and pull the rope, all you're doing is static stretches which won't do you much good.
Using a stretching aid to assist a stretch is fine as long as you take your time and don't use too much force (YMMV). In my experience, the very best aid for achieving progress in stretching (for limberness) is to perform a solid warm-up routine before hand.
Achieving a significant increase in limberness is something that takes time. If you push yourself to do too much, too fast you risk injury, and stretching-related injuries can undo any progress you've already made. Set realistic short and long term goals, and then make slow methodical progress towards those goals.