Method for the analysis of N-glycans attached to immunoglobulin G from human blood plasma in order to calculate Glycan Age Index; where method comprising the following steps: (i) quantitative analysis of released glycans: F A2B, F A2G2, F A2BG2, with the following chemical structures: where: F A2B ( GP 6): R1= GlcNAc; R2, R3, R4= H F A2G2: R1= H; R2, R3= Gal; R4= H F A2BG2: R1= GlcNAc; R2, R3= Gal; R4= H and GlcNAc = N-acetylglucosamine Fuc = fucose Man = mannose NeuAc = N-acetylneuraminic acid Gal = galactose or corresponding N-glycopeptides obtained by digesting immunoglobulin G with help of trypsin enzyme, in which relative abundance of each glycan or corresponding N-glycopeptide is obtained by normalization performed by dividing surface underneath the signal of every of the above mentioned glycans or corresponding N-glycopeptides with total surface of all signals of glycans or corresponding N-glycopeptides from the sample, giving values 〈 GP6 〉, 〈 GP14 〉, and 〈 GP15 〉 that represent corresponding relative abundances of the glycans F A2B, F A2G2 and F A2BG2 for an individual; where said quantitative analysis is performed with one of the methods selected from the group consisting of: ultra-performance liquid chromatography, MALDI-TOF mass spectrometry, liquid chromatography-mass spectrometry or capillary electrophoresis; and (ii) using the obtained values of relative abundances of the glycans 〈 GP6 〉, 〈 GP14 〉, and 〈 GP15 〉 for an individual in step for the calculation of Glycan Age Index, expressed in years and determined according to the following formulas in relation to the individual's sex, where said formulas are based on previously statistically evaluated data: GAI F = 75.4 + 135.3 ⋅ 〈 GP 6 〉 − 63.3 ⋅ 〈 GP 6 〉 2 − 1.1 ⋅ 〈 GP 14 〉 + 3.7 ⋅ 〈 GP 15 〉 for female sex; GAI M = 80.2 + 79.8 ⋅ 〈 GP 6 〉 − 25.1 ⋅ 〈 GP 6 〉 2 − 2.6 ⋅ 〈 GP 14 〉 + 6.7 ⋅ 〈 GP 15 〉 for male sex. (i) quantitative analysis of released glycans: F A2B, F A2G2, F A2BG2, with the following chemical structures: where: F A2B ( GP 6): R1= GlcNAc; R2, R3, R4= H F A2G2: R1= H; R2, R3= Gal; R4= H F A2BG2: R1= GlcNAc; R2, R3= Gal; R4= H and GlcNAc = N-acetylglucosamine Fuc = fucose Man = mannose NeuAc = N-acetylneuraminic acid Gal = galactose or corresponding N-glycopeptides obtained by digesting immunoglobulin G with help of trypsin enzyme, in which relative abundance of each glycan or corresponding N-glycopeptide is obtained by normalization performed by dividing surface underneath the signal of every of the above mentioned glycans or corresponding N-glycopeptides with total surface of all signals of glycans or corresponding N-glycopeptides from the sample, giving values 〈 GP6 〉, 〈 GP14 〉, and 〈 GP15 〉 that represent corresponding relative abundances of the glycans F A2B, F A2G2 and F A2BG2 for an individual; where said quantitative analysis is performed with one of the methods selected from the group consisting of: ultra-performance liquid chromatography, MALDI-TOF mass spectrometry, liquid chromatography-mass spectrometry or capillary electrophoresis; and GlcNAc = N-acetylglucosamine Fuc = fucose Man = mannose NeuAc = N-acetylneuraminic acid Gal = galactose (ii) using the obtained values of relative abundances of the glycans 〈 GP6 〉, 〈 GP14 〉, and 〈 GP15 〉 for an individual in step for the calculation of Glycan Age Index, expressed in years and determined according to the following formulas in relation to the individual's sex, where said formulas are based on previously statistically evaluated data: GAI F = 75.4 + 135.3 ⋅ 〈 GP 6 〉 − 63.3 ⋅ 〈 GP 6 〉 2 − 1.1 ⋅ 〈 GP 14 〉 + 3.7 ⋅ 〈 GP 15 〉 for female sex; GAI M = 80.2 + 79.8 ⋅ 〈 GP 6 〉 − 25.1 ⋅ 〈 GP 6 〉 2 − 2.6 ⋅ 〈 GP 14 〉 + 6.7 ⋅ 〈 GP 15 〉 for male sex.