That statement is not backed by any science, and the study even used 18+ healthy men and they also showed increases in natural test as good as the older folk. AFAIK I don't think anyone frowns on DAA, we frown in 18 year olds or under 21 folk that want to use it as a means to getting more out of it than it is (just a test booster) and we recommend that they just stick to diet and training. I've seen people (myself included) frowning upon it's use to counteract Early Age Low Testosterone problems, since that should be attended by an specialist to fix the underlying issue causing it.
Point being DAA and NMDA are some of the best Testosterone boosters around, effective and in case of sides a good AI like Erase and some Prolactin Control like Inhibit-P should be MORE than enough...
Other good (and bad) test boosters will be chimed in by many more reps, just read up on the literature behind them and make sure they have studies for humans and not rats only.