who had the highest batting average at age 18 minimum 300 pa

Ty Cobb has the highest career batting average by a player 18 or older when making 300+ plate appearances, with an average of .371.

	NAME	AVG	PA	G	AB	R	H	2B	3B	HR	RBI	BB	HBP	SO	SB	CS	TB	XBH	SH	SF	IBB	GIDP	OBP	SLG	OPS
1	Ty Cobb T. Cobb	.371	11,900	2,745	10,329	2,083	3,828	674	276	110		1,216	86		820		5,384	1,060	269				.441	.521	.962
2	Rogers Hornsby R. Hornsby	.359	9,477	2,259	8,172	1,579	2,930	541	169	301		1,041	48	677	135		4,712	1,011	216				.434	.577	1.011
3	Joe Jackson J. Jackson	.356	5,693	1,332	4,979	873	1,771	308	168	54		522	60		203		2,577	530	132				.423	.518	.941
4	Lefty O'Doul L. O'Doul	.349	3,658	970	3,264	624	1,140	175	41	113		333	22	123	36		1,736	329	39				.413	.532	.945
5	Tristram Speaker T. Speaker	.345	11,991	2,785	10,179	1,881	3,512	794	221	117		1,393	105		437		5,099	1,132	314				.429	.501	.930
6	Ted Williams T. Williams	.344	9,788	2,292	7,706	1,799	2,654	525	71	521	1,839	2,018	39	709	24	5	4,884	1,117	5	20	89	201	.482	.634	1.115
7	Babe Ruth B. Ruth	.342	10,622	2,504	8,400	2,173	2,873	506	136	714	2,213	2,062	44	1,331	123		5,793	1,356	116				.474	.690	1.164
8	Harry Heilmann H. Heilmann	.341	8,964	2,146	7,794	1,291	2,661	543	152	183		857	39	556	113		4,057	878	274				.409	.521	.930
9	Bill Terry B. Terry	.341	7,108	1,720	6,427	1,121	2,193	373	112	154	1,081	535	9	449	56		3,252	639	137				.393	.506	.899
10	Lou Gehrig L. Gehrig	.340	9,664	2,164	8,001	1,888	2,721	534	163	493	1,998	1,511	46	789	102		5,060	1,190	106			2	.448	.632	1.080
11	George Sisler G. Sisler	.340	9,012	2,054	8,270	1,281	2,810	425	164	102		467	48	327	375		3,869	691	227				.378	.468	.846
12	Tony Gwynn T. Gwynn	.338	10,232	2,440	9,288	1,383	3,141	543	85	135	1,138	790	24	434	319	125	4,259	763	45	85	203	259	.388	.459	.847
13	Riggs Stephenson R. Stephenson	.336	5,135	1,309	4,509	715	1,515	321	54	63	774	493	41	247	54		2,133	438	92				.406	.473	.879
14	Showboat Fisher S. Fisher	.335	384	138	340	62	114	21	6	8	71	37	1	35	6		171	35	6				.402	.503	.905
15	Al Simmons A. Simmons	.334	9,518	2,215	8,759	1,507	2,928	539	149	307	1,834	618	30	737	88		4,686	995	111			23	.380	.535	.915
16	Maurice Archdeacon M. Archdeacon	.333	449	128	384	84	128	14	4	0	29	48	4	39	13		150	18	13				.413	.391	.803
17	Paul Waner P. Waner	.333	10,766	2,550	9,460	1,627	3,152	605	191	113	1,316	1,093	38	376	104		4,478	909	175			45	.404	.473	.878
18	Eddie Collins E. Collins	.333	12,035	2,804	9,914	1,820	3,302	438	186	47		1,532	77		740		4,253	671	512				.426	.429	.855
19	Dale Alexander D. Alexander	.331	2,736	662	2,451	369	811	164	30	61	457	247	6	199	20		1,218	255	32				.393	.497	.890
20	Stan Musial S. Musial	.331	12,718	3,026	10,971	1,949	3,630	726	177	475	1,950	1,605	53	698	78	31	6,135	1,378	36	53	127	249	.417	.559	.976
21	Heinie Manush H. Manush	.330	8,420	2,009	7,657	1,288	2,526	491	160	110	1,183	507	70	346	113		3,667	761	186			1	.377	.479	.856
22	Ray Grimes R. Grimes	.329	1,787	433	1,536	269	505	101	25	27	266	204	17	133	21		737	153	30				.413	.480	.893
23	Wade Boggs W. Boggs	.328	10,740	2,439	9,180	1,513	3,010	578	61	118	1,014	1,412	23	745	24	35	4,064	757	29	96	180	236	.415	.443	.858
24	Rod Carew R. Carew	.328	10,550	2,469	9,315	1,424	3,053	445	112	92	1,015	1,018	25	1,028	353	187	3,998	649	128	64	144	217	.393	.429	.822
25	Bob Fothergill B. Fothergill	.325	3,581	1,105	3,270	452	1,064	225	52	36	581	202	22	179	42		1,501	313	87				.369	.459	.828