I have been competing for about 15 years and started incorporating TI about 6 years ago. My results are similar to what Dave and you report. I still need to use a quiet flutter kick on the 50,100 and 200m to be competitive. Once I get into 400 and 800 I am competitive with a 2 beat kick. I still kick vigorously on the last lap of any race.
The TI practice has resulted in my times coming down in all distances. At 74 I am beginning to level off in the 50, 100 and 200 races but the 400 and 800 are still coming down.
Am really working on flip turns, dolphin kicking off the wall and breakouts.
At your age you have wonderful years of fun swimming ahead. Enjoy the ride.
May we swim with ease at the speeds we choose.