Barry Bonds and Hank Aaron are tied for the oldest with 40+ home runs in a season. They were 39 years old.

Interpreted as:

oldest season with 40 or more hr by a player

	NAME	AGE	HR	SEASON	TM	G	AB	R	H	2B	3B	RBI	BB	HBP	SO	SB	CS	PA	TB	XBH	SH	SF	IBB	GIDP	AVG	OBP	SLG	OPS	WRC	WRAA	WOBA	WRC+	BRAA
1	Barry Bonds B. Bonds	39	45	2004	SFG	147	373	129	135	27	3	101	232	9	41	6	1	617	303	75	0	3	120	5	.362	.609	.812	1.422	185	108	.537	233	105.7
2	Hank Aaron H. Aaron	39	40	1973	ATL	120	392	84	118	12	1	96	68	1	51	1	1	465	252	53	0	4	13	7	.301	.402	.643	1.045	97	46	.449	176	40.8
3	Nelson Cruz N. Cruz	38	41	2019	MIN	120	454	81	141	26	0	108	56	7	131	0	1	520	290	67	0	3	8	14	.311	.392	.639	1.031	109	43.8	.417	164	42.7
4	Barry Bonds B. Bonds	38	45	2003	SFG	130	390	111	133	22	1	90	148	10	58	7	0	550	292	68	0	2	61	7	.341	.529	.749	1.278	148	80.5	.503	212	79.4
5	Darrell Evans D. Evans	38	40	1985	DET	151	505	81	125	17	0	94	85	1	85	0	4	594	262	57	1	2	12	5	.248	.356	.519	.875	96	28.1	.378	137	26.4
6	Barry Bonds B. Bonds	37	46	2002	SFG	143	403	117	149	31	2	110	198	9	47	9	2	612	322	79	0	2	68	4	.370	.582	.799	1.381	183	110	.544	244	109.9
7	Rafael Palmeiro R. Palmeiro	37	43	2002	TEX	155	546	99	149	34	0	105	104	6	94	2	0	663	312	77	0	7	16	10	.273	.391	.571	.962	121	41.8	.402	143	34.9
8	Andres Galarraga A. Galarraga	37	44	1998	ATL	153	555	103	169	27	1	121	63	25	146	7	6	648	330	72	0	5	11	8	.305	.397	.595	.991	127	47.2	.418	156	46.2
9	Hank Aaron H. Aaron	37	47	1971	ATL	139	495	95	162	22	3	118	71	2	58	1	1	573	331	72	0	5	21	9	.327	.410	.669	1.079	124	65.3	.466	191	57.2
10	Hank Sauer H. Sauer	37	41	1954	CHC	142	520	98	150	18	1	103	70	6	68	2	1	605	293	60	2	7		8	.288	.375	.563	.938	108	39.2	.417	138	29.4
11	Babe Ruth B. Ruth	37	41	1932	NYY	133	457	120	156	13	5	137	130	2	62	2	2	589	302	59	0				.341	.489	.661	1.150	153	79.1	.501	192	75.3
12	Nelson Cruz N. Cruz	36	43	2016	SEA	155	589	96	169	27	1	105	62	9	159	2	0	667	327	71	0	7	5	15	.287	.360	.555	.915	114	35.8	.383	148	38.2
13	Barry Bonds B. Bonds	36	73	2001	SFG	153	476	129	156	32	2	137	177	9	93	13	3	664	411	107	0	2	35	5	.328	.515	.863	1.379	200	117.7	.537	234	116.6
14	Rafael Palmeiro R. Palmeiro	36	47	2001	TEX	160	600	98	164	33	0	123	101	7	90	1	1	714	338	80	0	6	8	8	.273	.381	.563	.944	130	41.3	.396	139	35.4
15	Andres Galarraga A. Galarraga	36	41	1997	COL	154	600	120	191	31	3	140	54	17	141	15	8	674	351	75	0	3	2	16	.318	.389	.585	.974	131	47.8	.418	131	26.2
16	Babe Ruth B. Ruth	36	46	1931	NYY	145	534	149	199	31	3	162	128	1	51	5	4	663	374	80	0				.373	.495	.700	1.195	181	98.6	.525	206	95.1
17	Albert Pujols A. Pujols	35	40	2015	LAA	157	602	85	147	22	0	95	50	6	72	5	3	661	289	62	0	3	10	15	.244	.307	.480	.787	85	10.5	.333	114	10.6
18	Jim Thome J. Thome	35	42	2006	CWS	143	490	108	141	26	0	109	107	6	147	0	0	610	293	68	0	7	12	4	.288	.416	.598	1.014	123	46.5	.421	152	41.3
19	Frank Thomas F. Thomas	35	42	2003	CWS	153	546	87	146	35	0	105	100	12	115	0	0	662	307	77	0	4	4	11	.267	.390	.562	.952	123	42.2	.404	147	38.9
20	Barry Bonds B. Bonds	35	49	2000	SFG	143	480	129	147	28	4	106	117	3	77	11	3	607	330	81	0	7	22	6	.306	.440	.688	1.127	141	61	.456	174	61.2
21	Mark McGwire M. McGwire	35	65	1999	STL	153	521	118	145	21	1	147	133	2	141	0	0	661	363	87	0	5	21	12	.278	.424	.697	1.120	150	64.2	.453	169	61.5
22	Andres Galarraga A. Galarraga	35	47	1996	COL	159	626	119	190	39	3	150	40	17	157	18	8	691	376	89	0	8	3	6	.304	.357	.601	.958	128	39.4	.402	123	20.5
23	Hank Aaron H. Aaron	35	44	1969	ATL	147	547	100	164	30	3	97	87	2	47	9	10	639	332	77	0	3	19	14	.300	.396	.607	1.003	126	58	.435	170	51.3
24	Johnny Mize J. Mize	35	40	1948	NYG	152	560	110	162	26	4	125	94	4	37	4		658	316	70	0			7	.289	.395	.564	.959	126	47.9	.435	154	43.8
25	Hank Greenberg H. Greenberg	35	44	1946	DET	142	523	90	145	29	5	127	80	0	88	5	1	604	316	78	1			17	.277	.373	.604	.977	115	51.5	.446	165	44.8