Thru age 25, Trout has a 172 OPS+ while Mantle had 174. Trout had 54.2 WAR (and 9.2 per 650 PAs) while Mantle had 52.8 (and 8.8 per 650 PAs). So perhaps Trout is just slightly better.
But one thing that Trout has yet to match is Mantle's peak value in hitting. Look at what Mantle did at age 24. The table below shows he had a 210 OPS+ (his triple crown year). Age 25 was better with 221. He batted .365 with a .512 OBP and a .665 SLG.
Age
|
Trout
|
Mantle
|
19
|
89
|
117
|
20
|
168
|
162
|
21
|
179
|
144
|
22
|
168
|
158
|
23
|
176
|
180
|
24
|
173
|
210
|
25
|
186
|
221
|
Thru 25
|
172
|
174
|
So far Trout's best OPS+ was 186, last year. Mantle had one more season over 200, a 206. He also had a 195 and 188 (for qualified seasons). So his five best seasons are all above Trout's so far.
This year, after 54 games (one third of the season), Trout is at 207. Given that Mantle went over 200 three times, it seems like Trout would need to have at least one such season to be considered "another Mantle." Trout may end up with more career WAR (Mantle had 110.3) or a higher OPS+ (Mantle finished at 172). But Trout has not come close to Mantle's peak hitting value.
Last year Trout seemed to have a good chance to finish with a 200 or higher OPS+. Here is an excerpt from a post I did on August 8, 2017:
"Trout currently has an OPS+ of 216. He has played 68 games and the Angels have 49 left. Assuming an equal number of PAs per game played for each group of games (which might not be quite right), if he has an OPS+ of 178 the rest of the way, he would finish at 200"Trout had been hurt. That is why he had only played 68 games thru Aug. 7. At that point, his OPS was 1.180. But in his last 46 games, his OPS was "only" .907. Maybe his injuries slowed him down. So there is no guarantee he will finish with an OPS+ of 200 or higher this year even though he is off to a good start.