I think 400s for a 17 year old is low. As we have already stated to OP should investigate to make sure he is fine. His igf and t should be at prime numbers at 17. If he feels there’s something wrong should investigate.
If op wants to try a few things to increase his t naturally and then do labs, that’s good.
Teenagers should be seeing crazy high T levels and then the slow declined as one ages. I think guys are seeing 17 and freaking out about shutting this young man down when in reality he is low for his age.
President Trump is 72 years old and scoring virtually the same range. More testing is worthwhile. Guys seem to start having problems when dipping below 10.0 on Free T, he is well on his way.
Man if you feel good, have quality libido/erections and feel fine in general it doesn’t matter if you have a T level of 200, some people naturally only produce smaller amounts of testosterone and that’s all their body needs to maintain optimal function, who gives a fuck about the numbers it’s about symptoms. I’ll go off on a limb here and say if a 17 y/o has a good lifestyle, has A TT level in the 400s accompanied by symptoms he should be looked at as he may need TRT. Im 17 and I’m on trt (although granted I was way lower than 400) but the same rule applies. One with a low level shouldn’t just hop on trt though, it’s important to find out the cause of the low testosterone as it may be reversible, if a cause can’t be found then TRT is an option, however it’s very important to find out why one has low T as other problems may be present (pituitary tumour etc)